A female suicide bomber detonated a device in front of the car carrying Sri Lanka's top military general. (Sri Lanka Army /Associated Press)

Thousands of people have fled their homes in northeastern Sri Lanka as the military launches air strikes against the Tamil Tiger rebels.

At least 15 civilians have died since the military strikes began on Tuesday. An estimated 40,000 people are moving north to seek safety in the jungle.

The strikes are in response to a suicide attack on the government army headquarters, which killed at least eight people.

The strikes are the first official military action against the Tigers since the two sides reached a truce in 2002.

Tuesday's bombing also injured Sri Lanka's army's commander, Lt.-Gen. Sarath Fonseka.

It is believed a suicide bomber, pretending to be pregnant, blew herself up inside the army headquarters, one of the most secure places in the country.

The military says Fonseka has been undergoing surgery and is out of danger.

Violence continues despite truce

Tamil Tigers have been fighting to establish a separate state for minority Tamils in Sri Lanka's north and east for the past two decades.

The rebels and government reached a truce in 2002, but violence has continued.

Peace talks were supposed to take place in Switzerland this week, but arrangements became deadlocked on over how to transport a group of eastern rebel commanders to attend a pre-talks meeting.

Swedish Maj.-Gen. Ulf Henricsson, who heads the UN monitoring mission that oversees the truce, says if air strikes continue, peace talks will become difficult. He says the worst-case scenario is a return to civil war.

"There is still a valid ceasefire agreement, no party has ended it," he said.

The Sri Lanka government says it is still committed to a negotiated settlement to the long-running Tamil separatist conflict.