Syrian troops and militia fought fierce battles with Islamic State fighters in Syria's northeast overnight, a group monitoring the war said on Wednesday, as both sides vie for control of territory near the Iraqi frontier.
The battles took place near a prison just south of Hasaka city after Islamic State set off a bomb close by, the British-based Syrian Observatory for Human Rights said.
The surrounding Hasaka province, the country's northeastern triangle bordering on Turkey and Iraq, is a strategic area because it links up Islamic State-held land in Syria and Iraq.
The province is mainly populated by Syrian Kurds, whose own forces have also fought heavy battles against the al Qaeda offshoot across northern Syria. The Kurds say they do not coordinate their operations with the Syrian military but have worked with U.S.-led air forces bombing Islamic State.
The United States and its allies have launched 10 air strikes against Islamic State targets in Iraq and five in Syria since Monday morning, the U.S. military said on Tuesday.
The five strikes in Syria were concentrated near Hasaka and Kobani further to West, and hit tactical units, fighting positions, a command and control facility and a weapons cache, it said.
The Observatory, which collects its information from a network of sources on the ground, said around 30 fighters from the Syrian military and allied militia had been killed in five days of battles with Islamic State in Hasaka province .
State news agency SANA said late on Tuesday that the army had "eliminated" a large number of Islamic State fighters in the Hasaka countryside and foiled an attack on military outposts in rural areas in the east and southwest.
Clashes led to "dozens of members of Daesh being killed and wounded and the destruction of the terrorists' vehicles, weapons and ammunition," it said, using an Arabic acronym for Islamic State.
Steady advances by insurgents on key fronts in Syria have increased military pressure on President Bashar al-Assad, whose government increasingly sees western areas near the capital and the coast as its priority in the four-year-old conflict.