Airstrikes conducted by a U.S.-led coalition in Iraq and Syria against the Islamic State group is having a “devastating” effect and have “taken more than half” of ISIS’s leadership, Stuart Jones, the U.S. ambassador to Iraq, told Al Arabiya News Channel, in an interview aired Thursday. The news comes after the U.S. was reportedly criticized by the Iraqi government for not doing “enough” to eliminate the Sunni militant group.

“We estimate that the airstrikes have now killed more than 6,000 ISIS fighters in Syria and Iraq,” Jones reportedly said, adding that the airstrikes had also destroyed over a thousand ISIS vehicles in Iraq.

Jones said that the statistics were “not so important in themselves,” but “they do show the degradation of ISIS” and the group’s “inability to supply forces inside Iraq,” according to Al Arabiya News.

Meanwhile, U.S. Secretary of State John Kerry arrived in London to host talks with foreign ministers from 21 of the 60 countries involved in the international coalition against ISIS on Thursday.

"Terrorists want to drive us apart, but in fact their actions have had the opposite effect, they're bringing us together... with greater determination, greater resolve to be able to get the job done. And that is precisely what we're going to talk about in London," Kerry said, according to Agence France-Presse.

"We need to move ahead on every single front, militarily, but also through law enforcement, through intelligence sharing, by attacking the root causes so that terrorist appeals fall flat and foreign recruits are no longer enticed to go a place and wreak havoc on it."