British Prime Minister Tony Blair is expected to call for Iran and Syria to back efforts to stop violence in Iraq in an annual speech on foreign policy today.
The US and Britain are reviewing their strategy in response to growing opposition to their involvement there.
According to the text of his planned speech, due to take place later today, Mr Blair will argue the need for what he calls a "whole Middle East" strategy in which Damascus and Tehran help to crack down on terrorism in Iraq and the broader region.
"Just as the situation (in Iraq) is evolving, so our strategy should evolve to meet it," the speech says.
Mr Blair will also clarify that say Britain's policy on Syria and Iran has not changed: they must both renounce terrorism and in the case of Tehran, its nuclear ambitions.
But the British prime minister's official spokesman said the timing of his message was crucial, given "a recalibration of the American view" following last week's mid-term elections in the US in which the Democrats seized both houses of Congress.
President George W. Bush in the past has spurned engaging Iran and Syria and, only on Saturday, the White House branded Iran as part of a "global nexus of terrorism". But US officials now say they are open to all new ideas on Iraq.
Iran said today it was ready to consider any official US request to hold talks. "If they really want to hold talks with Iran, they should officially propose it and then Iran will review it," Foreign Ministry spokesman Mohammad Ali Hosseini said.
However, diplomats said it would be difficult for the US and Britain to seek Iranian help over Iraq at the same time as they are pushing for United Nations' sanctions against Tehran over its nuclear programme.
Mr Blair will say a broad strategy for the region must start with addressing the Israeli-Palestinian conflict.
Then Iran should be given a "strategic choice": "they stop supporting terrorism in Lebanon or Iraq; and they abide by, not flout, their international obligations," Blair will say. "In that case, a new partnership is possible."
The consequences of not doing so are "isolation", he will add. Syria faces a similar choice, Mr Blair's spokesman said.
Australian Prime Minister John Howard, a staunch US ally, said today he was in favour of talking to countries such as Syria and Iran about ending violence in Iraq.
A British government source said the Iraq and nuclear issues were separate. "We are trying to impress on Iran that a stable Iraq is to (its) benefit. The nuclear issue is ongoing and that's got to be addressed separately. You can't simply stop discussion of any other topics," the source said.
The Democrats are pledging a push to begin withdrawing US troops from Iraq in the next few months. Mr Blair also faces demands to set a timetable for withdrawal of British troops.