In this Tuesday, Sept. 23, 2014 photo released by the U.S. Air Force, a formation of U.S. Navy F-18E Super Hornets leaves after receiving fuel from a KC-135 Stratotanker over northern Iraq, as part of U.S. led coalition airstrikes on the Islamic State group and other targets in Syria.
Bombs over Syria
01:59 - Source: CNN

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NEW: More than 40 were killed in clashes across Syria, observers say

At least 30 airstrikes target Raqqa overnight, according to opposition activist group

Attacks mark increase in activity in Raqqa, which ISIS had made its de facto capital

CNN  — 

The U.S.-led coalition fighting ISIS in Syria has stepped up its attacks on the militant Islamist group’s de facto capital, with 30 airstrikes targeting Raqqa overnight, the London-based Syrian Observatory for Human Rights said Sunday.

Separately, another opposition activist group based in Raqqa reported that about 30 airstrikes by “the crusader alliance” targeted areas northwest of the city.

Previously, coalition strikes have primarily targeted Kobani, near the Turkey border. The attacks in Raqqa mark an increase in coalition activity there.

Last week, almost 100 people were killed in Syrian government airstrikes in Raqqa, the observatory said. Many more were critically injured.

Government warplanes carried out at least 10 airstrikes in Raqqa, targeting the city’s al-Hani Mosque and the public souk, or market, the observatory said, using reports from activists and residents on the ground.

Extremists have made the city, which sits on the banks of the Euphrates River, the de facto capital of their self-declared Islamic State that stretches across large areas of Syria and Iraq.

The city is known as a place where ISIS puts training centers, weapons depots and accommodations for fighters.

During the Syrian conflict, the group has also seized military bases from the Syrian regime near the city and in the wider Raqqa province.

Syria has been embroiled in a three-year civil war, with government troops battling ISIS and other rebels.

Fighting raged across the country on Sunday, the observatory said, with more than 40 people reported dead in airstrikes, shelling and raids.

A leader of al Qaeda affiliate Jabhat al-Nusra was among those killed in clashes north of Aleppo, the observatory said.

The Islamist militant group, also known as al-Nusra Front, is also trying to establish an Islamic state, though primarily in Syria.

It has been gaining ground and has emerged as one of the most effective groups fighting the Syrian regime during the civil war, drawing on foreign fighters with combat experience in Iraq and elsewhere.

At least 40 fighters killed in Syrian city of Kobani

CNN’s Ray Sanchez, Laura Smith-Spark, Mohammed Tawfeeq, Anas Hamdan, Holly Yan and Catherine E. Shoichet contributed to this report.