It was the latest in a string of attacks inside rebel territory using Claymore mines as roadside bombs that the rebels have blamed on government troops, who are using the Tigers' own deadly methods against them as a 25-year civil war escalates.

K Sivanesan, an MP with the rebel-backed Tamil National Alliance (TNA), was driving near his home in Mankulam in the Tigers' de facto state in the far north of the island when the blast occurred, killing him and his driver, his party said.

"It was an Army deep penetration unit," rebel military spokesman Rasiah Ilanthiraiyan said by telephone. "His vehicle was precisely targeted, because there were several vehicles travelling along this road."

"It's another example of how the regime in Colombo acts."

The military had no immediate comment.

Sivanesan had attended a meeting in Parliament on Wednesday.

"He left the parliament quarters after attending the parliament sessions yesterday," said fellow MP Suresh Premachandran.

"Most probably in those areas the Army is deploying deep penetration units," he added. "This fellow is a victim of that."

The attack came as Sri Lanka's government faced a barrage of criticism over its human rights record.

Human Rights Watch issued a report on Thursday accusing the government of being responsible for widespread abductions and disappearances as it fights the Tigers, which the government denies.

And a panel of international experts observing a Sri Lankan investigation into a raft of human rights abuses and killings said on Thursday it was quitting Sri Lanka, accusing the government of hindering the process and saying the probe was seriously flawed.

Analysts say the military has the upper hand in the latest phase of the long-running war given superior air power, strength of numbers and swathes of terrain captured in the island's east.

But they still see no clear winner on the horizon.

An estimated 70,000 people have died since the civil war began in 1983.