Barack Obama has made an unannounced visit to Iraq to meet US troops. He told them the next 18 months would be a "critical period" as the country prepares for the withdrawal of US troops by the August 2010 deadline. "You will be critical in terms of us being able to make sure Iraq is stable, that it is not a safe haven for terrorists, and we can start bringing our folks home," he told troops at Camp Victory. US officials said Mr Obama is also to have talks with Iraqi President Jalal Talabani and Prime Minister Nouri al-Maliki. White House spokesman Robert Gibbs said Mr Obama made the trip for "several important reasons, not the least of which is to see and spend some time with the men and women who are serving our country honorably here". Mr Obama made the visit after flying out of Istanbul, the last stop on his first major foreign tour which has also taken in the G20 summit in London and the Nato summit in Strasbourg.