WASHINGTON (AFP) - President Barack Obama will announce his decision on a timetable for withdrawing US troops from Iraq this week, upholding a campaign pledge, said Vice-President Joe Biden. "The President's going to make an announcement on Friday (tomorrow) - I believe it's Friday, or very soon," Biden told NBC Wednesday, amid reports that Obama would withdraw US combat forces from Iraq by August 2010. Obama "will speak to it in detail, and I think the American public will understand exactly what we're doing and I think they'll be pleased," Biden said. "We're keeping a campaign commitment," he added. A defence official had told AFP that the White House was weighing several options for US troop withdrawals from Iraq, with timetables ranging from Obama's 16-month campaign pledge to a 23-month option. A 19-month scenario was also presented to the president by military advisers. "The President has made no final decisions about Iraq," said White House spokesman Robert Gibbs, without however denying that an announcement was imminent. The Pentagon declined to comment on the reports that Obama has opted for a somewhat slower exit from Iraq than promised during the campaign. "We obviously have been involved in those discussions, provided any number of thoughts on how one might do that, timelines associated with that, the risks associated with various timelines," said Pentagon spokesman Bryan Whitman. "But now it's really up to the commander-in-chief at this point in terms of what he decides to do," he said.