COLOMBO, March 10: The Sri Lankan navy sank a Tamil Tiger rebel ship suspected of smuggling weapons on Monday, killing 11 on board after an exchange of fire off the island’s northeast coast that also wounded four sailors.

The incident, the deadliest since a ceasefire was signed last February and the second at sea in the past two months — comes as the two sides prepare for a sixth round of talks to end their 19-year war.

“Eleven of our cadres, including the ship’s captain, were killed when the vessel caught fire and sank after being attacked by the Sri Lanka Navy,” rebel political wing leader S.P. Thamilselvan said in an open letter to the defence minister.

“The incident occurred in international waters beyond the jurisdiction of the Sri Lanka Navy... We wish to emphasize that this grave incident will have far reaching implications for the peace process,” the letter said.

The Navy said it acted in self-defence after it tried to stop the boat, having received intelligence it was carrying arms. The ship was approaching the island’s northeast coast when the incident occurred, the Navy said.

“We asked the ship to stop and it didn’t, so then we started firing across the bow to warn them. They started firing back, and four of our men are injured,” navy spokesman Jayantha Perera told Reuters.

The Liberation Tigers of Tamil Eelam, who have been fighting for a separate state for minority Tamils in the north and east, denied their ship was smuggling arms and asked the defence minister to convey their “deep displeasure” over the clash.

Nordic monitors overseeing the truce said it was too early to say what impact the clash would have on next week’s talks in Japan.

“We sincerely hope the talks continue as planned,” said Hagrup Haukland, the deputy head of the monitors.

“They (the LTTE) are very much concerned because this incident happened in international waters. They are looking very, very seriously upon it,” he said.

Last month’s fifth round of talks was overshadowed by the suicides of three rebels who blew up their boat after being caught by the Navy with a cache of weapons. Two truce monitors jumped overboard to escape the explosion after boarding the boat to investigate.

Under the terms of the ceasefire agreement neither side is allowed to move military equipment into areas controlled by the other, although they are allowed to maintain their forces.

A local newspaper reported on Sunday the rebels had attempted to procure Russian weapons through the Russian embassy in Laos.

The capital Colombo was also on alert for violence on Monday, as opposition parties held one of the largest protests against the government since the peace process began. Some critics say the government is giving away too much to the rebels.

Police said they deployed extra forces and troops were on standby, but the estimated 40,000 marchers protested peacefully against concessions to the rebels and the cost of living.

“The peace process they have launched, we have no faith in. The north and east are being handed over to the LTTE. Not that we are against peace, but the peace which will divide the country,” said opposition People’s Alliance member Nimal Siripala de Silva.—Reuters