Sri Lanka's military says its elite police force has seized a key Tamil Tiger rebel base in the country's east.

Military spokesman Brigadier Prasad Samarasinghe says the police commandos from the Special Task Force overran the base in Ampara district and seized a weapons cache.

In a separate incident, the military says rebels blew up an electrical transformer on the outskirts of the capital, Colombo, disrupting power supplies in the area.

Meanwhile, the military is on high alert following two separate deadly bomb attacks on buses last week. At least 21 people were killed in the attacks and dozens of others injured.

Authorities blame Tamil Tiger rebels for both blasts, but rebel officials deny the charges.

The military has stepped up its campaign against the rebels, conducting four days of consecutive air strikes against rebel targets last week.

Despite a 2002 ceasefire deal, renewed violence has erupted between the government and Tamil rebels fighting for an independent homeland.

Some 67,000 people have died during the conflict, including 3,000 last year.