Bush and Ban were to hold talks at 1:00 pm (1700 GMT), one day after the US president, in a fresh Middle East peace push, called for an international conference grouping Israel, the Palestinians, and some of their Arab neighbors.

Asked about the agenda for the meeting, Bush spokesman Tony Snow said they would discuss that new initiative, Sudan's Darfur province, Iran's contested nuclear program, unrest in Lebanon, climate change, and other issues.

"Obviously Darfur continues to be a concern," he told reporters. "The president appreciates his diplomacy. The one thing that we want is vigorous international action in response to genocide."

"There will be an expression of concern about Iran's continued defiance of UN Security Council resolutions," said Snow, amid concern among US lawmakers that Bush is weighing possible military options against the Islamic republic.

The United States last week expressed skepticism of Tehran's agreement to allow inspectors from the UN nuclear watchdog agency, the International Atomic Energy Agency, access to a heavy-water reactor under construction at Arak.

Iran agreed to let UN inspectors visit the reactor by the end of July, as part of a series of measures aimed at clearing up questions over Tehran's nuclear program.

The UN Security Council has imposed two rounds of sanctions to get Tehran to cease enriching uranium, to stop building Arak -- where Iran has blocked access since April -- and to cooperate fully with IAEA inspectors.

Iran insists its nuclear program is a peaceful effort to generate electricity, but the United States fears it is a cover for atomic weapons building.

Heavy water reactors produce plutonium, which can be used to make nuclear weapons. The other main atom bomb material is enriched uranium.

Iran and the IAEA are to hold a fresh round of talks in Vienna on July 25 and 26.

Bush and Ban were also to discuss the Middle East peace process after the Islamist Palestinian movement Hamas seized Gaza from backers moderate Palestinian president Mahmud Abbas on June 15.

They were also expected to discuss increased international aid for Afghanistan and Iraq; efforts to battle climate change; and "concern about Syria's role with regard to the government of Lebanon," said Snow.

"So it's going to be a very wide-ranging conversation," the spokesman said.

Ban on Monday warned against any "abrupt" withdrawal of American troops from Iraq amid a fierce debate on the issue in the US Congress and significant support from the war-weary US public for calling US forces home.

"The international community cannot and should abandon them," Ban told a press conference. "Any abrupt withdrawal or decision may lead to a further deterioration of the situation in Iraq."

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