Pilots and ground crew prepared combat aircraft Panavia Tornados at RAF Marham Wednesday in the United Kingdom. WPA Pool/Getty Images

The U.S.-led airstrike campaign against the Islamic State militant group will last for “at least” three years, U.K. Defense Secretary Michael Fallon said Thursday. The campaign was “not going to be quick,” he said, and American military officials had projected warplanes could still be dropping bombs in Syria after 2017.

“The American estimate of the campaign in Iraq, which began last year, was that it would last at least three years and we’re not halfway through that yet,” Fallon told BBC Radio 4’s "Today" program. “The operations there by the coalition have lasted just over a year and the [U.K.] prime minister has been pretty clear that this is going to be a long campaign to ensure that Daesh are thrown out of Iraq and that they are degraded and defeated in eastern Syria. This is not going to be quick,” he said, using another name for the terrorist organization also known as ISIS and ISIL.

The United States began conducting airstrikes against ISIS in Syria and Iraq in August 2014. The United Kingdom joined the campaign that September. The 62-nation U.S.-led coalition has since carried out more than 6,400 airstrikes against ISIS targets. U.S. officials have estimated the bombing campaign has eliminated 10,000 of the group’s Sunni militants, Sputnik News reported.

Fallon said Thursday it was not “likely” Western ground troops would be deployed because it would “radicalize the Sunni tribes even more.”

British warplanes launched airstrikes in Syria within hours of a parliamentary vote Wednesday that authorized an extension of the bombing to the Middle Eastern country. Fallon said four Tornado jets equipped with Paveway bombs hit seven targets in eastern Syrian oilfields and had “dealt a real blow” to the ISIS-controlled area, the Guardian reported.

ISIS captured international headlines in June 2014 when it took over the vital northwest Iraqi city of Mosul. The group currently controls about a third of Iraq and Syria.