Before dawn on Friday, US-led coalition aircraft reportedly destroyed the main water pipeline supplying the Syrian city of Raqqa, the so-called "Islamic State's" (IS) de facto capital located in northern Syria.

Two bridges linking the city's southern flank to the countryside were also destroyed during ground-fighting between US-backed fighters and IS militants, observers reported Friday.

The Britain-based Syrian Observatory for Human Rights, which relies on a network of on-the-ground activists to track Syria's war, reported clashes between IS fighters and the US-backed Kurdish-led Syria Democratic Forces (SDF) north of the city.

The observatory said the US-led coalition has been providing air cover to SDF fighters during Friday's fighting.

The United States and its allies have been targeting IS in and around Raqqa for more than two years. US-backed Kurdish-led fighters have led the ground offensive across the region, mostly north of the city. IS has held the city since January 2014.

The latest attacks echo those conducted in Iraq late last year when government forces mounted an offensive to recapture the Iraqi city of Mosul from jihadis. Destroying bridges makes it difficult for IS fighters to move through the city, but critics complain that the negative effects are worse for civilians.

Raqqa under siege

SANA, the Syrian state news agency, and an IS-affiliated website reported early Friday that Raqqa's main water pipeline was damaged in an airstrike, cutting off the city's water supply.

The IS-affiliated website also reported that the only two bridges crossing the Euphrates River at the southern tip of the city have been destroyed.

A local media collective - Raqqa is Being Slaughtered Silently - also reported the lost water supply, and criticized the destruction of the two bridges, saying they are used by civilians. They called such acts "absolutely unacceptable." They said the water supply is fully cut from the city.

"It seems that the US-led coalition is trying to besiege civilians of Raqqa by destroying the infrastructure," the group said on Twitter.

The US-led coalition did not immediately respond to questions about targeting the water pipeline.

More than 200,000 people are believed to be still living in Raqqa.

bik/sms (AP, dpa, Reuters)