Democratic presidential hopeful Barack Obama, citing the legacy of Abraham Lincoln, pledged yesterday to bridge the partisan gridlock in Washington, end the war in Iraq and transform American politics as the first black US president.

Launching his 2008 White House campaign outside the building in where Lincoln began his fight against slavery with a famous 1858 speech that declared "a house divided against itself cannot stand," Obama said it was time to "turn the page" to a new politics.

"Let us begin this hard work together. Let us transform this nation," Obama, 45, told a cheering crowd of supporters in Springfield, Illinois, who braved sub-freezing temperatures outside the old state capital building.

Obama's candidacy has intrigued Democrats looking for a fresh face and sparked waves of publicity and grass-roots buzz about the first black presidential candidate seen as having a chance to capture the White House.

The freshman senator from Illinois has faced questions and doubts about his relative lack of experience, his policy views on a wide range of issues and on whether the United States is ready to elect a black man to the White House. Obama acknowledged the questions about his experience.