BAGHDAD — America's top military leader arrived in Iraq on Saturday, state television reported, making his first visit to the country since a U.S.-led coalition began a campaign of airstrikes targeting the extremist Islamic State group (ISIS).

The visit by Army Gen. Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, was not previously announced. It came just two days after he told Congress that the United States would consider dispatching a modest number of American forces to fight with Iraqi troops against the Islamic State group, which controls about a third of Iraq and neighboring Syria.

The Iraqi military and security forces, trained by the U.S. at the cost of billions of dollars, melted away in the face of the extremist group's stunning offensive this summer, when it captured most of northern and western Iraq, including the country's second-largest city Mosul.

Dempsey said Thursday that Iraqi forces were doing a better job now, although an effort to move into Mosul or to restore the border with Syria would require more complex operations.

He also told the U.S. House Armed Services Committee that America has a modest force in Iraq now, and that "any expansion of that, I think, would be equally modest."

"I just don't foresee a circumstance when it would be in our interest to take this fight on ourselves with a large military contingent," he said.

Dempsey's visit comes just one day after Iraqi forces drove Islamic State militants out of a strategic oil refinery town north of Baghdad, scoring their biggest battlefield victory yet.

The recapture of Beiji is the latest in a series of setbacks for the jihadi group, which has lost hundreds of fighters to U.S.-led coalition airstrikes in Iraq and Syria, particularly in the group's stalled advance on the Syrian town of Kobani. On Friday, activists there reported significant progress by Kurdish fighters defending the town.

Meanwhile on Saturday, two parked car bombs exploded minutes apart north of Baghdad, targeting a checkpoint staffed by army soldiers and security forces, authorities said. The blast killed six people and wounded 25, police and hospital officials said. They spoke on condition of anonymity because they were not authorized to brief journalists.