Washington  - US President Barack Obama called Thursday for Israel and Hamas to adhere to their fragile ceasefire adopted last weekend after three weeks of fighting in the Gaza Strip.

Obama called on Israel to complete the pullout of its troops from Gaza and declared that Hamas must end rocket attacks.

He called for the opening of border crossings for commerce and humanitarian aid to flow into the territory, and emphasized that the United States remains committed to ensuring that Hamas cannot smuggle weapons into Gaza.

"Lasting peace requires more than a long ceasefire, and that's why I will sustain an active commitment to seek two states living side by side in peace and security," Obama said, reaffirming his commitment to press ahead with the peace process.

Obama's comments came as he announced his appointment of former senator George Mitchell as his special envoy for Middle East peace.

Mitchell, 75, of Maine rose to become leader of the centre-left Democrats in the US Senate. He later helped broker the peace deal in Northern Ireland as a special envoy for then-president Bill Clinton.

Mitchell will now be taking on the challenge of advancing the peace process amid a fragile truce between Israel and Palestinian militant group Hamas, in the wake of three weeks of fighting in the Gaza Strip.

"I don't underestimate the difficulty of this assignment. The situation in the Middle East is volatile, complex and dangerous," Mitchell said. "But the president and the secretary of state have made it clear that danger and difficulty cannot cause the United States to turn away."

Mitchell will soon travel to the Middle East to help ensure that the Gaza ceasefire will be lasting, Obama said, adding that Israel has a right to defend itself against rocket attacks by Hamas, which controls Gaza.

"No democracy can tolerate such danger to its people, nor should the international community, and neither should the Palestinian people themselves, whose interests are only set back by acts of terror," Obama said.

The United States would fully back an international donor conference for short-term humanitarian assistance and long-term reconstruction for the Palestinian economy under the auspices of the Palestinian Authority, Obama said, while deploring the humanitarian conditions in the tiny Palestinian enclave.

"Our hearts go out to Palestinian civilians who are in need of immediate food, clean water and basic medical care, and who've faced suffocating poverty for far too long," Obama said.

During his first full day in office, Obama telephoned Wednesday with Israeli Prime Minister Ehud Olmert, Palestinian President Mahmoud Abbas, Jordanian King Abdullah and Egyptian President Hosny Mubarak. In her first day on the job, Secretary of State Hillary Rodham Clinton followed up with calls to Olmert and Abbas.

Israel launched a massive assault in Gaza in response to Hamas rocket attacks. During three weeks of fighting, more than 1,400 Palestinians were killed while 13 Israelis died. (dpa)