Rival Palestinian leaders from the Fatah and Hamas groups formally ended a bitter, four-year rift Wednesday, but Israel’s prime minister denounced their reconciliation as a “tremendous blow to peace” and a “victory for terrorism.”

Fatah’s leader, Palestinian President Mahmoud Abbas, told a ceremony in the Egyptian capital, Cairo, that Palestinians have forever turned the “black page of division.” He promised to soon visit the Hamas-run Gaza Strip.

Hamas chief Khaled Meshaal said the two groups seek a common goal – a Palestinian state with Jerusalem as its capital and no Israeli settlers. He said Palestinians should not give up “a single inch of land” or the right of return for Palestinian refugees.

The accord calls for the formation of an interim Palestinian government followed by presidential and legislative elections within a year.

The two Palestinian factions split in 2007 amid fighting over Fatah officials being removed from power in Gaza. Israel responded by placing the territory under an economic blockade.

Israeli leaders say the new agreement could derail peace talks between Israel and the Palestinians.

Prime Minister Benjamin Netanyahu held talks with his British counterpart in London Wednesday. He urged David Cameron not to recognize the Fatah-Hamas government. Mr. Netanyahu will meet Thursday with French President Nicolas Sarkozy.

U.S. President Barack Obama will host Mr. Netanyahu May 20 at the White House.

State Department spokesman Mark Toner said Wednesday that Washington continues to believe Hamas must recognize Israel’s right to exist, reject violence and abide by interim peace agreements if it wants to play a meaningful role in the political process.

He said the United States will look at the formation of any new Palestinian government before taking steps on future aid. The presence of Hamas politicians in the new governing structures could mean a cutoff in U.S. aid to the Palestinian Authority.

The U.S., Israel and the European Union all consider Hamas a terrorist group.

In an early sign of change on the ground, Hamas’ al-Aqsa television was permitted to broadcast for the first time since 2007 in the West Bank and the Fatah-controlled Palestine television into Gaza.

In Gaza City, thousands turned out to celebrate the deal. Some waved yellow Fatah flags, which had been banned for the past four years.

The outgoing head of Israel’s Shin Bet internal security service, Yuval Diskin, predicted the unity deal will not last long. He also said Israel is prepared to maintain its cooperation with Mr. Abbas’ security service.

For now, while a committee negotiates the future of security cooperation and prisoners, Fatah and Hamas will police their own areas independently.