US President George W. Bush said on Thursday that there can be no delay in Iraq's elections scheduled for Jan. 30, rejecting calls to postpone the elections until security in Iraq is improved.

"It's time for Iraqi citizens to go to the polls," Bush said in a joint briefing with visiting Nigerian President Olusegun Obasanjo at the White House.

Bush said he had personally approved an expansion of US troop levels in Iraq ahead of the elections.

He predicted that Iraq's elections will leave the world "amazed that a society has been transformed so quickly."

Bush also referred to the election crisis in Ukraine, saying there should be no foreign influence in its future presidential elections.

If there is to be a new election, as many government leaders and Ukrainian demonstrators have demanded, it "ought to be free from any foreign influence," Bush added.