The following clarification was printed in the Guardian's Corrections and clarifications column, Thursday 29 January 2009

In the article below we said that George Mitchell, who has recently been appointed as Barack Obama's Middle East envoy, successfully completed the task of overseeing the decommissioning of weapons in the Northern Ireland peace process. To clarify: Mitchell was chair of the international body whose 1996 report suggested that decommissioning of paramilitary weapons should take place at the same time as all-party negotiations and he chaired the peace talks that led to the Good Friday agreement in 1998 in which the participants reaffirmed their commitment to the total disarmament of all paramilitary organisations. In 2005 the Independent International Commission on Decommissioning headed by General John de Chastelain reported that the IRA had completed disarmament.

President Barack Obama yesterday promised the US will "actively and aggressively" work for an elusive Middle East peace deal and will dispatch a high-powered envoy to the region as a matter of urgency.

Speaking to diplomats at the state department on his second day in office, he set out his widely-awaited views on the Israeli-Palestinian conflict, ending the near silence he had maintained over the last few weeks.

Putting the conflict at the heart of US foreign policy for the first time in eight years, he said he would invest time, political capital and cash in the peace effort.

Intent on reshaping foreign policy as quickly as possible, he named the veteran mediator George Mitchell as his Middle East envoy. He also named another veteran diplomat, Richard Holbrooke, as his special envoy to Pakistan and Afghanistan.

He pledged to continue US support for Israel but his tone was more balanced than that of George Bush, who uncritically sided with Israel.

Obama, speaking alongside his secretary of state, Hillary Clinton, called for a durable ceasefire in Gaza. He urged Hamas to stop firing rockets into Israel, as Bush had done, but he also called on Israel to "complete the withdrawal of its forces from Gaza".

The president expressed concern at the loss of life among Israelis and Palestinians, and at the suffering in Gaza. He said his heart went out to "civilians who are going without food, water or medical care".

He said he would help Egypt to try to curb smuggling of weapons through underground tunnels to Gaza and would also provide and seek donations from other countries for the development of Gaza.

Obama's promise of intervention comes at a time when feelings are running high in the region over the high death toll in Gaza. Though there is a ceasefire in place, it remains fragile.

It is also a politically difficult time in the region, with Israelis scheduled to go to the polls next month and the Palestinians badly divided.

Palestinian President Mahmoud Abbas, welcomed Obama's comments but a Hamas spokesman in Beirut, Osama Hamdan, told al-Jazeera that Obama's comments did not represent change and, unless he did so, he would be doomed to the same failure as Bush.

Obama signalled a willingness to pick up from where President Bill Clinton left off. Clinton tried to broker a peace deal in 2000 and 20001 between the then Palestinian president Yasser Arafat and the then Israeli prime minister, Ehud Barak, but ran out of time.

Bush only intermittently engaged in the Middle East, choosing to side almost uncritically with Israel. He held a peace conference at Annapolis, Maryland, in 2007, but failed to throw his weight behind it.

At the state department, Obama confirmed that Mitchell, 75, the former senator, whose appointment had been leaked to the press this week, would be his Middle East envoy.

Mitchell, appointed by Bill Clinton to help as a mediator in the Northern Ireland peace process, played a pivotal role in Belfast.

He won the respect of both the IRA and the Loyalist paramilitaries for his efforts at bringing about decommissioning. He also reported to Bill Clinton on the Israeli-Palestinian conflict, calling for the Palestinian authority to crack down on militant groups but for Israel too to freeze the expansion of Jewish settlements on the West Bank.

Mitchell told diplomats at the state department: "I believe deeply that with committed persevering and patient diplomacy peace and stability can be achieved in the Middle East."

The appointment of Mitchell undercuts the role of Tony Blair, who since 2007 has been working as a Middle East mediator of the Quartet, which is made up of the UN, the US, the EU and Russia. But Blair yesterday welcomed Mitchell's appointment. A spokesman for Blair said it would renew their close and productive relationship in Northern Ireland. "It shows the true commitment President Obama and Secretary Clinton have to making real progress in the Middle East," the spokesman said.

As well as naming Mitchell, Obama and Clinton yesterday confirmed that Holbrooke, 67, another veteran of the Bill Clinton administration who was US ambassador to the United Nations and brokered the Bosnia peace agreement, is to be a special envoy to Afghanistan and Pakistan.

Holbrooke said Americans and their foreign partners in Afghanistan were fighting "a ruthless and determined enemy without any scruples at all, an enemy that is willing to behead women who dare to teach in a school to young girls, an enemy that has done some of the most odious things on Earth. And across the border lurks the greater enemy still: the people who committed the atrocities of 11 September 2001."