UNITED NATIONS (AP) — The Palestinians on Tuesday urged the United Nations to pressure Israel to allow Palestinian refugees caught in the Syrian conflict to travel to the West Bank and Gaza, saying Israel "has callously rejected this appeal."

Israel's "intransigence can neither be accepted nor justified" and should not be allowed "to prevent us from bringing our refugees to safety in their own homeland," Palestinian U.N. Ambassador Riyad Mansour said in identical letters to the Security Council, General Assembly and secretary-general.

It was not clear whether this was the first time the Palestinians have asked for such help. Such a move would greatly increase the 4.5 million population of the Palestinian territories, which could have an impact on future negotiations on a two-state solution.

Mansour said at least 480,000 Palestinian refugees remain in Syria, with more than half displaced from their refugee camps and 95 percent in need of humanitarian assistance.

Many are in the Yarmouk refugee camp on the outskirts of the Syrian capital Damascus. U.N. officials have said they have not been able to reach the camp since March. The Islamic State extremist group entered the camp in early April. U.N. officials last month reported several suspected cases of typhoid among people from the camp.

"Rather than being forced to flee in desperation to neighboring countries or to attempt the treacherous journey to leave the Middle East region entirely in search of safety, stability and livelihoods, the Palestine refugees should be allowed to join their brothers and sisters in their homeland," Mansour wrote.

He urged the U.N. and the international community to support the effort to bring the refugees to the Palestinian territories "as a matter of humanitarian, moral and political urgency." He said an estimated 80,000 Palestinian refugees have already fled Syria, whose war is now well into its fifth year.

The spokesman for Secretary-General Ban Ki-moon, Stephane Dujarric, said they had just received the letter and had no immediate comment.

Spokespeople for the Palestinian mission to the U.N. and for Israel's U.N. mission did not immediately respond to a request for comment.

The U.N. agency for Palestinian refugees, the U.N. Relief and Works Agency, says the Palestinian refugee camps in Syria were established in 1948, the year of Israel's creation and Palestinian displacement.