Sri Lanka's President Mahinda Rajapaksa on Thursday pledged safe passage for thousands of people trapped by fighting between government forces and Tamil Tiger rebels in the north.

Mr. Rajapaksa also urged the Tamil separatists to allow civilians to move to safety within the next 48 hours.

Hours earlier, the United Nations said it had evacuated hundreds of wounded civilians, including 50 children, from the war zone after allegedly being blocked for two days by the rebels. A Tamil Tiger official quoted on a pro-rebel Web site denied the allegation.

The U.N. High Commissioner for Human Rights, Navi Pillay, accused both Sri Lankan troops and Tamil Tiger rebels of committing grave violations. She stressed that civilians must be allowed to flee conflict areas.

Humanitarian groups say hundreds of civilians have been killed and 250,000 others have been trapped by the conflict. Sri Lanka says those numbers are inaccurate.

Also Thursday, police in the southern Indian state of Tamil Nadu said a Tamil man set himself on fire to protest against civilian casualties and Sri Lanka's military offensive against the Tamil rebels.  

Authorities say the man doused himself in kerosene and set himself ablaze in the streets of Chennai, the state capital. More than 55 million Tamils live in Tamil Nadu.  

In an ongoing offensive, the Sri Lankan military has captured key rebel strongholds, forcing the remaining Tiger fighters into a small jungle area in the northeast.

Tamil Tiger rebels have been fighting since 1983 to establish an independent homeland for Sri Lanka's Tamil minority. More than 70,000 people have died in the conflict.

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