Sri Lanka's military said it has killed at least 20 Tamil rebels during heavy fighting in the country's north, as part of an ongoing assault on key rebel territory.

A military statement said troops captured the village of Sinna Paranthan, northwest of the rebels' de facto capital of Kilinochchi, on Tuesday. The statement said its fighter jets launched several air strikes against rebel positions again Wednesday in the northern Paranthan and Muahamalai areas.

The rebel-affiliated Web site TamilNet said military air strikes hit a convent marked with a large red cross on its roof Tuesday. It said the strikes killed 85 cows near the convent and sent civilians fleeing from the area.

Independent verification of either side's claims is impossible because journalists are barred from entering the conflict zone.

The Tamil Tigers have been fighting since 1983 to establish an independent homeland for Sri Lanka's Tamil minority in the island's north. The conflict has killed more than 70,000 people.

The New York-based Human Rights Watch organization said Tuesday that Sri Lanka's government is restricting essential humanitarian aid to some 200,000 civilians displaced by the fighting.

The group called on the government to allow aid groups back into the affected regions. It said civilians displaced in these war zones face severe shortages of food, shelter, water and sanitation supplies. 

Some information for this report was provided by AFP and AP.