"What's going on in the land of the Palestine serves only the enemies of the Islamic nation," King Abdullah told Abbas, according to the Saudi News Agency. "If it continues, it will rob the Palestinians of the fruits of their long struggle."
Leaders of the respective groups arrived in Saudi Arabia Tuesday for talks aimed at ending factional warfare that has killed roughly 80 people since December and forming a unity government to end a Western embargo.
Upon his arrival in Jeddah, Abbas entered talks with the Saudi king, while a Hamas delegation led by Damascus-based chief Khaled Mashaal was set to meet with Abdullah later before the talks begin either late Tuesday or Wednesday.
Jamal al-Shobaki, Palestinian ambassador to Saudi Arabia, said a deal was crucial.
"They will not leave this holy place without an agreement, because things are catastrophic on the ground and the whole world will turn its back on us if we continue that way," al-Shobaki told Reuters.
But Mashaal's deputy, Moussa Abu Marzouk, was more hesitant about the outcome when he spoke with the Associated Press shortly before leaving Damascus for the talks.
"The disagreements on forming a national unity government ... have become narrower," Marzouk said, "but we don't know whether an agreement will be reached or not."
Tensions have spiraled in the Gaza Strip since Hamas, an Islamist group whose charter calls for Israel's destruction, took control of the Cabinet and the legislature last year, prompting the West to suspend aid unless the group moderates its stance.
Earlier attempts to stop the bloodshed and find common political ground have resulted in short-lived cease-fires and a threat by Abbas to call a new election, which Hamas said would be the equivalent of a coup.
Abbas, a moderate whose presidential guard receives training and non-lethal equipment from U.S. funds, said he would give the talks one last chance.
The United States and Israel hope that any unity government will recognize the Jewish state and abide by interim peace deals brokered before Hamas' electoral victory.
The presence of the Saudi king and princes at Tuesday's talks show the kingdom's will to repair the rift between the two factions. Iran has provided financial aid to the Hamas-led government and Saudi fears the non-Arab Shiite Muslim country is increasing its influence.