The US says rebels have tried to set up roadblocks in the city, which is on the main road from Baghdad to north Iraq.
It also said US forces had to diffuse a possible car bomb. Samarra residents said US warplanes bombed the city as tanks rolled through the streets.
Samarra is one of several areas in Iraq which have fallen under the control of rebel forces in recent months.
In Falluja, another rebel stronghold, the US reported carrying out an airstrike on a hideout of followers of a rebel leader.
The Americans and Iraq's temporary government say they are determined to retake rebel-held areas before elections in the country in January.
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