Prime Minister Gordon Brown held "very cordial and constructive" talks with US President George Bush on Monday, his official spokesman has said
Talks between the two men were "cordial and constructive".
The "lengthy" video conference is thought to have focused on Iraq.
It came after US Commander General David Petraeus told the US Congress he believed a drawdown of US troops could begin by the middle of next year.
Defence Secretary Des Browne briefed the UK's Cabinet on Gen Petraeus's report at their Tuesday meeting.
The discussion between Mr Brown and Mr Bush is first officially disclosed direct contact between the two men since July.
It follows last week's decision to withdraw 550 UK soldiers from central Basra to join 5,000 troops at an airbase outside the city, taking up an "overwatch" role.
Gen Petraeus told Congress he believed the US would be able to reduce troop levels by about 30,000 to pre-surge numbers by next summer.
The prime minister's spokesman said: "We are working very closely with the Americans.
"The prime minister had a lengthy discussion with President Bush yesterday in one of their regular video conferences.
"We will work very closely with them ... The decision in relation to our troops in Basra will be based on an assessment by our military commanders of the situation on the ground."
And he said: "The general approach being taken by the US and the UK is entirely consistent. Conditions in the south are different from those elsewhere."
The spokesman stressed that the Americans had been fully consulted over the British pull-out from Basra City.
He said there had been no change in the British position on Iraq as a result of Gen Petraeus' report.
Mr Brown told the Cabinet that Britain had a responsibility to fulfil its commitments and obligations to the Iraqi people.
He said the three priorities now were security, encouraging political reconciliation and giving the Iraqi people a stake in their own future.
Mr Browne told the Cabinet that the current security situation in Basra was "stable" and that the withdrawal from Basra Palace had been completed "smoothly".
Mr Brown is due to make a statement on Iraq to the House of Commons soon after MPs return from their summer recess on 8 October.