GEOFF BENNETT: This week, the U.S. ambassador to the U.N. is visiting the border of one of the world's worst crises.

More than five million Sudanese have been displaced by a power struggle between the military and an offshoot paramilitary group.

More than 200,000 people from Sudan's Darfur region have fled into Chad, where U.N.

Ambassador Linda Thomas-Greenfield announced new sanctions and additional humanitarian assistance.

Nick Schifrin spoke to her for a look at U.S. policy five months after violence in Sudan broke.

NICK SCHIFRIN: They crossed the border with their entire lives on the back of horse-drawn carts and walked dozens of miles carrying the next generation to a safer future.

Sudanese refugees arrived by the thousands into Chad and were greeted yesterday by U.S.

Ambassador to the U.N. Linda Thomas-Greenfield.

She pledged another $163 million in aid to families fleeing war.

Five months of infighting between Sudan's armed forces and rebel Rapid Support Forces, or RSF, has engulfed Sudan's cities and reignited ethnic conflict in Darfur, a region the size of Spain.

Twenty years ago in Darfur, government-backed Janjaweed militias committed what the U.S. labeled genocide.

Those militias birthed the RSF, which, today, in the same place is alleged to have launched the same crimes.

NATHANIEL RAYMOND, Yale School of Public Health: We are talking hundreds of thousands of people who have really, at this point, no protection force between them and RSF, which has clearly shown, like the Janjaweed from which they are descended, that their intent is to liquidate non-Arab people in Darfur.

NICK SCHIFRIN: And to discuss the humanitarian crisis and U.S. policy towards Sudan, we turn to U.S.

Ambassador to the U.N. Linda Thomas-Greenfield.

Ambassador, thanks very much.

Welcome back to the "NewsHour."

You just heard one description of what these refugees that you have been speaking to are running from.

What did they tell you?

LINDA THOMAS-GREENFIELD, U.S.

Ambassador to the United Nations: They tell me that they ran because they were afraid.

They ran because they saw their neighbors, their friends, their family members killed in front of their eyes.

They were raped, as some of the women shared with us, and they were afraid for their future.

And they only -- their only hope was to seek refuge here in Chad.

NICK SCHIFRIN: As we said, much of this violence in Darfur is being committed by the RSF, which is a descendant of the Janjaweed militias who committed genocide 20 years ago in Darfur.

If the State Department today has evidence that this is the same group committing similar violence in the same place, let me ask you directly, is today's violence also a genocide?

LINDA THOMAS-GREENFIELD: Today's violence is very reminiscent of what we witnessed in 2003 and 2004.

We are gathering data and gathering information now.

As you know, we have already issued sanctions against one individual and visa restrictions on another one.

And we will continue to follow this situation very intensely and closely and develop our decision based on the facts on the ground.

NICK SCHIFRIN: You heard from Nathaniel Raymond, who is in the Sudan Observatory Group, which is funded by the State Department, who is trying to find some of the facts on the ground, earlier say that the RSF's intent is to liquidate non-Arab people in Darfur, like the Janjaweed did 20 years ago.

Do you believe that's the case?

LINDA THOMAS-GREENFIELD: I believe that we're seeing evidence of that.

NICK SCHIFRIN: And is that defined as ethnic cleansing?

LINDA THOMAS-GREENFIELD: No, we -- the people we're seeing crossing the border are definitely people of the same ethnic descent.

They're telling us the same stories of the attacks that are being made on their families, on their villages, on their livelihoods.

And as we gather that data, we will make firm decisions about what to do moving forward.

But, right now, we're holding every person that we are aware of accountable for what they are doing, and we will continue to do that.

NICK SCHIFRIN: Yesterday, you imposed sanctions on the deputy leader of the RSF, who is also the brother of the commander of the RSF, General Hemeti.

But some members of Congress want to see more.

Why are there not sanctions General Hemeti himself and, indeed, the head of the Sudan armed forces, General Burhan?

LINDA THOMAS-GREENFIELD: What you saw us announce yesterday was just the start part.

And we're continuing to gather data and put together the facts, so that we can move forward on other announcements.

NICK SCHIFRIN: On that effort to hold these parties accountable, is there a plan to escalate sanctions?

LINDA THOMAS-GREENFIELD: Certainly, there's a plan to continue to impose sanctions.

NICK SCHIFRIN: Twenty years ago, when the violence was raging in Darfur and the U.S. declared genocide, President Bush repeatedly raised what the Janjaweed militias were doing.

Why is President Biden not talking about Darfur?

LINDA THOMAS-GREENFIELD: This is what I -- I represent the face -- one of the faces of the administration.

I'm here because President Biden wanted me to be here.

And this is something that the administration is engaging on, and I'm part of that engagement.

NICK SCHIFRIN: Back then, as you know, the U.S. pushed resolutions through the Security Council that demanded the Janjaweed disarm.

The Security Council authorized troops, of course, to go into Darfur again.

Why is that not happening again?

Why aren't there more efforts by the Security Council to repeat those actions?

LINDA THOMAS-GREENFIELD: Well, you may know that I held as -- during my presidency of the Security Council during the month of August the first open meeting on Sudan.

And one of the things I heard during that meeting was that the press, the world was not paying enough attention.

And I made the decision that I would bring members of the press with me here, so that we can witness firsthand what was happening on this border.

So, our efforts in August were the start, and we certainly will continue to focus attention on this issue, and particularly in the Security Council.

I'm looking forward to returning to New York, where I can share with other members of the council what I witnessed here and push for more council action.

NICK SCHIFRIN: Some regional experts told me today that they thought Secretary-General Guterres was not aggressive enough on the topic of Sudan.

And one senior U.S. official told me that the -- quote -- told me that the U.N. had been -- quote -- "dysfunctional" on Sudan.

Do you agree?

LINDA THOMAS-GREENFIELD: Look, I have been here on the ground watching U.N. agencies responding, responding in ways that are indescribable to save lives.

I have walked with UNHCR employees and other U.N. agency employees who are devoting all of their efforts and their time to saving the lives of the people in Sudan.

So I will commend that effort here in Chad.

And I know that efforts are being made elsewhere to support the Sudanese who are the victims of this brutal war.

NICK SCHIFRIN: And, finally, let's talk about the regional actors.

The United Arab Emirates, in particular, has been a supporter of General Hemeti and the RSF, the Rapid Support Forces.

Has the U.S. confirmed that the UAE has sent weapons to the RSF in the last few months?

LINDA THOMAS-GREENFIELD: We have called for all countries who might be engaged in this war to cease those efforts.

We need to call for peace.

We need to encourage these -- the warring parties to put down their weapons.

We're supporting efforts to find a peaceful solution, to negotiate a peaceful settlement to this war, because, until this war ends, people in Sudan will continue to suffer.

And we have made very, very clear any countries that might be engaged in supporting the efforts of the warring parties should cease those efforts immediately.

NICK SCHIFRIN: Forgive me for asking again.

Has the UAE sent weapons to the RSF?

LINDA THOMAS-GREENFIELD: I can't confirm who is sending weapons to the RSF.

I can say that we know weapons are going in, and we want to urge those countries who are providing those weapons to cease those efforts.

NICK SCHIFRIN: And you are calling for those countries to cease those efforts.

On the other side, of course, we have Egypt, Saudi Arabia that have historically supported the Sudan armed forces.

What is the U.S. doing, beyond calling for those countries not to fuel the conflict, to stop fueling the conflict?

LINDA THOMAS-GREENFIELD: Well, you know that we have been very, very actively engaged in the peace process and trying to bring the parties to a negotiated settlement.

Those efforts are continuing.

We're supporting the efforts of the Arab League, of the African Union, and all of the regional parties who might be able to influence these warring parties.

And, today, I met with the president, the traditional president of Chad, and also urged that he continue to actively engage to stop this war.

NICK SCHIFRIN: Ambassador Linda Thomas-Greenfield, thank you very much.

LINDA THOMAS-GREENFIELD: Thank you.