The government of the Maldives says that a coastguard vessel has opened fire on a boat carrying suspected Tamil Tiger rebels from Sri Lanka.
There have been sea clashes between rebels and Sri Lankan navy
A spokesman said this followed a stand-off in Maldivian waters. The rebels have denied involvement.
He said the boat had been sunk and five people on board had been captured.
Despite a truce still being in place on paper, Sri Lanka has been sliding back towards civil war, with more than 4,000 people killed in the past 15 months.
The chief spokesman for the Maldives government Mohammed Hussain Sharif said the nearly 12-hour stand-off between its coastguard forces and the suspected rebel boat happened near an atoll, several hundred nautical miles south of the main archipelago.
He said it may have foiled an attempt by the rebels to smuggle arms to Sri Lanka.
The five people on board the boat were being questioned, the spokesman said.
The Maldives government says that one of those detained spoke Malayalam and not Tamil, and is suspected of being a guide for the others who are still being interrogated.
Mr Sharif said the Maldives vessel had been fired upon first, and one of those held had said the others were armed Tamil Tigers.
The Tamil Tigers military spokesman Rasiah Ilanthiraiyan has denied the rebels were involved in the incident.
"We are not operating in that area," Mr Ilanthiraiyan told the Reuters news agency from a rebel base in the north of Sri Lanka.
"These guys are not our people."
Earlier this month, a number of rebels were killed in a sea battle with the Sri Lankan navy off Sri Lanka's north-eastern coast.
The navy said it sank two Tamil Tiger boats, part of a flotilla of 26 rebel vessels, and killed at least 10 rebels.
The Tamil Tigers are fighting for an independent state in the north and east.
Clashes at sea and on land are now an almost daily occurrence. Both sides say they still respect the ceasefire and are responding to the other side's aggression.