WASHINGTON (Reuters) - The U.S. military on Thursday retreated from a top general’s claim this week that the number of foreign fighters joining Islamic State in Iraq and Syria has plummeted by as much as 90 percent.

A black flag belonging to the Islamic State is seen near the Syrian town of Kobani, as pictured from the Turkish-Syrian border near the southeastern town of Suruc in Sanliurfa province, in this file photo dated October 6, 2014. IREUTERS/Umit Bektas

Air Force Major General Peter Gersten, deputy commander for operations and intelligence in the U.S.-led coalition battling Islamic State, told reporters on Tuesday that the number of foreign fighters joining the group had fallen to 200 a month from between 1,500 and 2,000.

U.S. Army Colonel Steve Warren, a Baghdad-based spokesman for the coalition, told Reuters that the official estimate is higher than the one Gersten offered, although he did not provide a precise figure.

“We believe the foreign fighter flow was 2,000 at one point and is now down to a quarter or less of that,” Warren said. That would equal roughly 500 fighters per month, or a drop of about 75 percent from the peak.

“The key is the cumulative effect over time of the damage we have done to them on the battlefield combined with reduced (foreign fighter) flow, so they have to increasingly use younger fighters, conscripts, and security/governance personnel to field their force,” he said.

It was unclear why Gersten used a figure of 200.

U.S. officials, speaking on condition of anonymity had questioned Gersten’s remarks. There are multiple signs that the tide of foreign fighters has abated but not that dramatically, they said.

The United States and its allies have long tried to track the flow of foreign fighters - which a top Obama aide last week said totaled 40,000 over the war’s course - in part because of worries that some could return to conduct attacks in their home countries.

Authorities have said that several of the men behind last month’s deadly attacks in Belgium had traveled to Syria earlier.

U.S. officials caution that calculations about the number of foreign fighters joining Islamic State’s self-described “caliphate” are estimates at best.

Asked about Gersten’s figure of 200 at a U.S. Senate Armed Services Committee hearing on Thursday, Defense Secretary Ash Carter declined to repeat it.

“I think it’s very hard to be very precise about these numbers,” Carter said.

A U.S. intelligence official, speaking on condition of anonymity, said that intelligence estimates of foreign fighter flows are never given as single figures but only as a range. They “are very rough figures,” he said.

“Overall, there has been a significant decline in foreign fighters flow,” said a second U.S. intelligence official.

At one time, Islamic State had enough new recruits to replace about 1,000 killed per month, mostly with foreign fighters, the second U.S. intelligence official said. “They have fallen well below that number now.”