WASH INGTON (AFP) - US President Barack Obama on Tuesday hailed the withdrawal of US troops from Iraqi towns and cities as an important milestone, but warned difficult days lay ahead. The Iraqi people are rightfully treating this day as a cause for celebration, Obama said at the White House. This is an important step forward, as a sovereign and united Iraq continues to take control of its own destiny, Obama said, also hailing the pullback, agreed last year with the Iraqi government, as an important milestone. The President also warned that it was now up to Iraqs leaders to take political steps to bolster what the White House says are improving security conditions on the ground in Iraq. Iraqs leaders must now make some hard choices necessary to resolve key political questions to advance opportunity and provide security for their towns and their cities, Obama said. Make no mistake, there will be difficult days ahead. We know that the violence in Iraq will continue, we see that already in the senseless bombing in Kirkuk earlier today. There are those who will test Iraqs security forces and the resolve of the Iraqi people through more sectarian bombings and the murder of innocent civilians. I am confident that those forces will fail. Todays transition is further proof that those who have tried to pull Iraq into the abyss of disunion and civil war are on the wrong side of history.