WATCH: White House press secretary Jean-Pierre affirms Ukraine’s agency to decide when the war is over

With several European leaders meeting with Ukrainian President Volodymyr Zelenskyy and debate rising over how to end Ukraine’s war with Russia, the White House is reiterating President Joe Biden’s adage “nothing about Ukraine without Ukraine.”

Watch the briefing in the player above.

Biden has taken the position that he won’t pressure Zelenskyy to make concessions to Moscow to bring about an end to the war.

“President Zelenskyy is the democratically elected leader of that country and he, only he, gets to determine how this war ends,” said White House Press Secretary Karine Jean-Pierre.

“He gets to determine how he defines victory. And he gets to determine how the outcome will be,” she said.

Four European leaders expressed their support for Ukraine on Thursday while meeting with Zelenskyy, vowing to back Kyiv’s candidacy to eventually join the European Union and offering more weapons to fend off Russia’s invasion.

However, many Ukrainian fear that Western resolve could wane. France, Germany and Italy have all faced criticism for continuing to engage with Russian President Vladimir Putin – and failing to give Kyiv the amount of weaponry it says its needs.

The U.S. and its European allies have given billions of dollars in weaponry to Ukraine, and Germany and the U.S. recently announced new arms shipments. Such arms have been crucial in preventing the Russians from taking the capital, but Kyiv has said much more will be needed.

Ukrainian officials have expressed concern that “war fatigue” could eventually erode international support, especially as rising prices and upcoming U.S. elections increasingly dominating public concerns.

The White House is also expressing concern for two Americans in Ukraine, who are now missing after their group came under heavy fire in the Kharkiv region of northeastern Ukraine near the Russian border on June 9, leaving loved ones at home anxiously awaiting information about their whereabouts.

The U.S. State Department is investigating reports that Russian or Russian-backed separatist forces captured at least two American citizens, Alex Drueke and Andy Huynh.

Both are military veterans from Alabama. If captured, they would be the first Americans fighting for Ukraine known to have been captured since the war began.

The White House also described as a success a U.S.-led mission that captured a senior leader of the extremist Islamic State group in a military operation in northern Syria.