President Bush has warned that Iraq and Afghanistan could get more violent as elections in both countries approach.
Bush will address the United Nations this week
But he vowed to stand by the two countries and also to "accelerate the march of freedom in our world".
His comments, in his weekly radio address, came after a surge of attacks in Iraq raised doubts over whether its elections in January could go ahead.
Mr Bush's presidential challenger John Kerry accused him of preparing to call up extra troops after the US election.
"He won't tell us what congressional leaders are saying - that this administration is planning another substantial call-up of reservists and guard units immediately after the election," Mr Kerry said during a campaign stop in Albuquerque on Friday.
The accusation was based on information from Democratic Representative John Murtha, a member of the House Armed Services Committee, who said he had heard of the plans from Pentagon officials.
In his address on Saturday, Mr Bush said increasing violence in Iraq and Afghanistan would not deter him.
"Terrorist enemies are trying to stop the progress of both
those countries, and their violent and merciless attacks may
increase as elections draw near," he said.
"But all the world can be certain: America and our allies
will keep our commitments to the Afghan and Iraqi people."
Kerry claims Bush will call up more reserves
Mr Bush is scheduled to address the United Nations General Assembly on Tuesday.
He told his radio audience: "Never in the history of the United Nations have we faced
so many opportunities to create a safer world by building a
"For the sake of our common security, and for the sake of
our common values, the international community must rise to
this historic moment. And the United States is prepared to