Sri Lankan naval forces backed by helicopter gunships attacked a group of rebel boats early Tuesday, sinking two and killing six Tamil Tiger sailors, the military said.

The sea battle came as the military pushed ahead with its multi-pronged offensive against the rebels’ de facto state in the north.

The battle erupted in Nayaru Lagoon on Sri Lanka’s northeast coast, just south of the rebel stronghold of Mullaitivu, when navy forces attacked seven Tamil Tiger boats, the military said in a statement.

The navy sank two rebel boats and severely damaged a third, killing six rebel sailors, the military said.

As the remaining rebel boats fled to shore to be hauled out of the water, attack helicopters pounded them with airstrikes, it said.

The military also launched airstrikes in other parts of the north, sending helicopters to attack a rebel gathering point in Kilinochchi district early Tuesday, the military said.

It was not possible to contact rebel officials for comment because most communication lines with the north have been severed. Independent accounts are difficult to obtain from the battlefield because most journalists are barred from the war zone.

Meanwhile, ground battles continued across the war front, with troops attacking Tamil Tiger fighters in the Jaffna, Mullaitivu and Kilinochchi fronts and destroying several rebel bunkers, the military said.

In recent months, the government has pushed the rebels out of large swathes of territory they once held in the north and vowed to crush the group and end the island nation’s civil war.

The Tamil Tigers have fought since 1983 to create an independent state for the country’s ethnic minority Tamils, who have suffered marginalization by ethnic Sinhalese-controlled governments. More than 70,000 people have been killed in the violence.