The U.S.-led coalition fighting the Islamic State in Syria pounded the militant group’s de facto capital with as many as 30 airstrikes Sunday, activists told the Associated Press.

The strikes targeted the group, also known as ISIS or ISIL, in their stronghold of Raqqa, according to the Britain-based Syrian Observatory for Human Rights. The group said the strikes also targeted the Division 17 air base, which the Islamic State seized earlier this year from Iraqi government forces.

The U.S. military did not confirm the airstrikes to the Associated Press.

The monitoring group, which relies on a network of activists inside Syria, reported at least 30 coalition strikes in all. The Local Coordination Committees, an activist collective, also confirmed the airstrikes. Neither group had casualty figures.

The American-led coalition began targeting Islamic State militants in Syria in September, expanding an aerial campaign already hitting the extremist group in Iraq.

Many of the U.S. airstrikes in Syria have targeted Islamic State fighters who are attacking the predominantly Kurdish town of Kobani on the Turkish border.

The Observatory said that at least 50 Islamic State militants were killed on Saturday and early Sunday in clashes with Kurds and in coalition airstrikes. Eleven Kurdish fighters also were killed, according to the Observatory.

Idris Nassan, a Kurdish official from Kobani, said by telephone that tens of IS militants were killed, but he did not have a concrete figure.

IS has been attacking Kobani since mid-September. The militants' offensive has bogged down, and the Syrian Kurds — backed by their Iraqi brethren with heavy weapons — appear to have seized the momentum and to have begun pushing the jihadis back.

The report of the strikes came as a new Pentagon report revealed that the U.S. is conducting roughly 85 percent of the multi-national airstrikes against Islamic State in both countries.

U.S. fighter planes and drones have conducted 819 strikes, compared to 157 from the 10 other countries, according to the detailed report obtained last week by FoxNews.com.

The Associated Press contributed to this report.