BEIRUT -- The Syrian insurgency claimed Thursday to have near-total control of a strategically important province in the country's northeast, home to some of the few remaining domestic oil production facilities that supply fuel for President Bashar Assad's military forces, after ferocious clashes that lasted for three days.
The rebel assertions about the province, Hasaka, would, if confirmed, be at least the third significant gain by the insurgency this week, following the seizure of Syria's largest hydropower dam and the takeover of a northern military air base with much of its fleet still intact. Hasaka province includes the ethnically mixed city of Shadadi, one of the 10 largest cities in the nation.
In addition, rebels claimed to have shot down three Syrian air force warplanes Thursday, corroborating their assertions with videos posted online. If so, that would be the government's biggest one-day loss of warplanes to insurgent fire in the conflict, which began nearly two years ago as a peaceful protest to Mr. Assad's autocratic rule.
Hasaka, about 375 miles northeast of Damascus, borders Iraq and is one of Syria's richest provinces. It is the heart of Syria's oil-producing and grain-growing region and is home to a sizable share of the country's Kurdish minority.
The Syrian Observatory for Human Rights, an anti-Assad group based in Britain, said the rebel fighters were led by the Nusra Front, an Islamic militant group blacklisted by the United States for its suspected ties to al-Qaida in Iraq. The observatory said the Nusra Front had led a series of attacks on military and security posts in Hasaka, culminating in an assault on their bases in Shadadi. The observatory also said rebels had stormed the administration and housing buildings of Syrian Oil Co. workers at the al-Jabsa fields, the largest in the province, and now controlled those facilities.
At least 100 armed forces members were killed in Shadadi, the observatory said, while 30 Nusra fighters were killed, including five from Kuwait and Iraq.
An anti-Assad Syrian activist in the region reached by phone, Omar Abu Layla, said the loss of the al-Jabsa fields, he said, "is very important since they supply regime forces with oil needed to operate heavy equipment."