Colombo  - The death toll in a massacre of villagers by Tamil rebels in eastern Sri Lanka increased to 21 as the army and police stepped up security in the area, military officials said Sunday.

The military had reported late Saturday that eight civilians were killed in the attack, but a subsequent search overnight revealed that 21 persons including women and children were killed, they said.

Another 20 villagers were left wounded in the attack on Kirimetiya village in Inginiyagala district. Many of the villagers were belonged to the majority Sinhala community.

The attack followed an abortive attempt by rebels to carry out airstrikes on air force headquarters, during which two aircraft were downed by anti-aircraft fire, killing the two rebel pilots.

One of the aircraft crashed into a government building in Colombo close to the air force headquarters, and the other was brought down close to an air base in the outskirts of the capital.

Two civilians - a 14-year-old-girl and 23-year-old man - were killed by anti-aircraft fire from security forces. At least 53 others were injured where the two aircraft downed - some hit by security forces' fire.

The incidents came as government troops were continuing military operations in areas around the last rebel stronghold in the northeast of the country.

The rebels have been confined to an area of 90 square kilometers in the Mullaitivu district, according to the military.

Some 70,000 civilians are reported to be trapped in the area and the rebels have not allowed them to leave while 35,000 have already left into government controlled areas. dpa