WASHINGTON/BAGHDAD -  The US military believes that some 50,000 Islamic State fighters have been killed since the United States started battling the group more than two years ago, a senior US military official said on Thursday, calling it a "conservative estimate."

The official, who spoke to Pentagon reporters on condition of anonymity, said the figure showed how the United States was effectively combating the group with US-led coalition airpower and limited US troop deployments in support of local forces.

Meanwhile, Iraq's Joint Operations Command said Thursday that Iraqi aircraft struck dozens of mostly foreign fighters from the Islamic State group near the border with Syria the previous day.

It confirmed that deadly strikes in the Al-Qaim area in the west of the country were carried out by the Iraqi air force but described allegations by officials that dozens of civilians were killed as IS propaganda.

The JOC issued a statement confirming that the Iraqi air force had carried out two strikes in the militant-held Al-Qaim area on Wednesday, saying they targeted hideouts used by IS members.

It said the first one was conducted at 0900 GMT and struck a two-storey building housing 25 mostly foreign would-be suicide bombers, led by a fighter it named as Abu Maysar al-Kawkazi (from the Caucasus).

It said another strike was carried out during a second mission at 0955 GMT, hitting a building hosting 30 to 40 IS fighters, also mostly foreigners.

Iraqi officials, including parliament speaker Salim al-Juburi, had said on Wednesday that dozens of civilians were killed or wounded in a strike on a market area in Al-Qaim.

They blamed the government and demanded an investigation.

The JOC denied striking a market area and said a blast there was caused by a car bomb that either went off accidentally or was detonated by IS for propaganda purposes.

Amaq, an IS propaganda tool, released a video late Wednesday showing scenes of chaos in a market area, with bodies strewn across a street and wounded being treated.