Iraqi security forces south of Mosul
Iraqi security forces south of MosulReuters

Iraqi and U.S.-led coalition forces have killed or gravely wounded more than 2,000 Islamic State (ISIS) fighters in the battle for Mosul since October, the top U.S. commander in Iraq said Sunday, according to The Associated Press.

Lt. Gen. Stephen Townsend told reporters there are still an estimated 3,000 to 5,000 ISIS fighters defending Mosul. He applauded the efforts of Iraqi security forces, who began their offensive on October 17 in what has been billed a decisive phase of the anti-ISIS fight.

"By our calculations, we think we have killed or badly wounded over 2,000," Townsend said Sunday at a joint news conference with U.S. Defense Secretary Ashton Carter at Qayara air base, according to AP.

U.S. officials have declined to say how many Iraqi government troops have been killed in the Mosul fight.

Recapturing the city of Mosul, Iraq's second-largest, is crucial to the Iraqis' hopes of restoring their sovereignty, although political stability will likely remain a challenge afterward.

Iraqi forces have so far only won back a handful of eastern Mosul neighborhoods since launching the offensive in mid-October, noted AP.

Townsend disputed any suggestion that ISIS has managed to fight the Iraqi government forces to standstill in Mosul.

After citing the estimated 2,000 ISIS casualties, he added, according to AP, "I don't think that suggests anything about a stalemate. This is a major urban area. Any army on the planet, including the United States Army, would be challenged by this fight."

"The Iraqi army has come back from near-defeat two years ago, and now they are attacking this major city," Townsend continued. "I don't think there is anything in there about a stalemate."

Townsend said U.S. intelligence estimated before the Mosul campaign kicked off that ISIS had 3,500 to 6,000 fighters in the city. He said the current estimate is 3,000 to 5,000.

The comments come a day after Carter announced in Bahrain that he is sending another 200 troops to Syria to train and advise local fighters combatting ISIS. There are already 300 U.S. troops authorized for the Syria effort, and some 5,000 in Iraq.

Carter told an international security conference in Bahrain that the battle for Mosul and for the Syrian city of Raqqa, the de facto capital of ISIS’s self-described “caliphate”, would be crucial for defeating the group, which has claimed attacks worldwide.

"The seizure of these two cities is necessary to...put ISIL on an irreversible path to a lasting defeat," he said, according to AP, using the alternative acronym for ISIS.

He did not predict how long it might take for Iraqi forces to prevail in Mosul, but said he was “confident that ISIL's days in Mosul are numbered."

ISIS has called on its fighters not to back down from Mosul. Last month, the group’s leader, Abu Bakr al-Baghdadi, released a new audio recording in which he called on the people of Mosul to fight the "enemies of God".

Previously, ISIS released a video in which its fighters in Mosul predicted the Americans would run from the city “with your tail between your legs."