A pro-Tamil Tiger politician, Nadarajah Raviraj, has died in hospital after being shot by unidentified gunmen in the Sri Lankan capital, Colombo.
Mr Raviraj was an active parliamentarian
He was shot as he left his house in Colombo for work. One of his guards was also killed in the attack.
It is the latest incident in a week of heavy violence in Sri Lanka.
Dozens of civilians were killed by army shelling in the east on Wednesday. The navy and Tamil Tigers fought sea battles on Thursday and Friday.
The US assistant secretary for south and central Asian affairs, Richard Boucher, told reporters in neighbouring India that "we have growing concern" about the situation in Sri Lanka.
President Mahinda Rajapakse condemned the killing of Nadarajah Raviraj, calling it a "heinous act" by "those opposed to dissent and political pluralism in a democratic society".
Mr Raviraj represented the Tamil National Alliance (TNA) coalition from northern Jaffna district in parliament.
Mr Raviraj's car was riddled with bullets
The TNA is linked to the Tamil Tigers.
No-one has yet claimed responsibility for the killing for Mr Raviraj. But his colleagues blamed the government.
"It is government forces or forces aligned to the government, there can be no question," TNA leader R Sampanthan told the Reuters news agency.
"This is an attempt to stifle... and silence those who can justifiably espouse the Tamil cause."
A spokeswoman for the international truce monitors in Sri Lanka, Helen Olafsdottir, told the BBC's Newshour programme that there seemed to be total impunity regarding assassinations in Sri Lanka, which she said occurred everyday.
On Thursday Mr Raviraj, a former mayor of Jaffna, had taken part in a protest against the army shelling of a camp for displaced people in the eastern Vakarai district that led to thousands of Tamils trying to flee from the camp.
The military expressed regret over the deaths but accused the Tamil Tigers of using the civilians as human shields. International truce monitors said there was no evidence that the rebels had launched attacks from the camp.
Another TNA politician, Joseph Pararajasingham, was shot and killed by unidentified gunmen in Batticaloa, 300km (189 miles) east of the capital, Colombo, last December.
Meanwhile, there have been further clashes at sea between the navy and Tamil Tiger rebels in Sri Lanka, a navy spokesman says.
He said the navy had sunk two Tiger boats, killing a number of rebels, off the eastern district of Trincomalee.
On Thursday, the military said it had sunk 22 rebel boats and lost two of its own off the northern Jaffna peninsula. At least 20 sailors were missing following the clashes on Thursday.
The rebels say they lost five of their members, and that they killed at least 25 sailors and captured four more.