Beirut and Washington, Reuters—Islamic State of Iraq and Syria (ISIS) fighters seized a Syrian town back from Kurdish-led forces near Raqqa city on Monday, a group monitoring the war reported, recovering ground near its de facto capital two days after it was pummeled in heavy US-led airstrikes.

The Syrian Observatory for Human Rights said ISIS forces had taken Ain Issa and surrounding areas from the People’s Protection Units (YPG) militia, which only seized the town from ISIS control two weeks ago.

A spokesman for the YPG could not immediately be reached for comment, but had earlier reported an attack by large numbers of ISIS fighters on YPG positions in the area about 30 miles (50 kilometers) north of Raqqa city.

US officials said the airstrikes in Raqqa city over the weekend were some of the most intense to date against ISIS in Syria.

The Observatory said the attacks destroyed seven bridges over waterways in the city, which is bordered to the south by the Euphrates river, in a bid to curtail ISIS’s ability to move fighters and equipment.

Ain Issa, the town reportedly recaptured on Monday, sits on a major east–west highway that runs all the way from Aleppo in the west to the Iraqi city of Mosul.

The YPG-led forces captured Ain Issa on June 23, part of an offensive that drove deep into ISIS’s stronghold of Raqqa province. The YPG also captured the town of Tel Abyad at the Turkish border in the offensive.

The United States and its allies stepped up their campaign against ISIS with 38 airstrikes on targets belonging to the group in Iraq and Syria on Saturday, a joint command statement said on Sunday.

Eighteen of the strikes were near the Syrian city of Raqqa, capital of the “caliphate” that ISIS has declared.

The statement from the Combined Joint Task Force said tactical units and vehicles had been hit and 16 bridges had been destroyed. The attacks in Syria also included five near Al-Hasakah and three near Kobani, in which tactical units, vehicles and fighting positions were hit.

In Iraq, ISIS was targeted in 12 strikes near eight cities. The statement said tactical units, fighting and staging positions, weapons and vehicles had been hit.