The trooper died in a mine blast in the northern district of Vavuniya, the ministry said, adding that four soldiers were also wounded in another blast in the Jaffna peninsula, further north.

Security forces shot dead two Tiger rebels in the Jaffna peninsula Monday, the ministry added.

John Holmes, the under secretary general for humanitarian affairs and emergency relief coordinator, discussed the island's deepening Tamil separatist conflict and the plight of civilians caught in the crossfire.

He was due to travel to the northern and eastern regions, officials here said.

Holmes paid tribute to 17 aid workers of the French charity ACF, or Action Against Hunger, who were killed a year ago by unidentified gunmen in the restive northeast and reiterated a call for justice.

"I repeat the call of the secretary general to the government of Sri Lanka to investigate this murder with the full weight and force of the justice system," Holmes said in a speech, a copy of which was released to the press.

"This needs energy and a determination to find the truth."

The remembrance ceremony at the United Nations compound in Colombo was declared off limits for journalists without explanation. However, local media reported pressure from the Sri Lankan government to keep the event low profile.

The ACF said in a statement that remembrance ceremonies were held in Colombo, in the island's northeast as well as in Paris for the 13 men and four women killed a year ago.

Nordic truce monitors have blamed government forces for the killings, a charge denied by the Sri Lankan authorities. Police investigations remain inconclusive.

Thousands have been killed in fighting between troops and the Liberation Tigers of Tamil Eelam since December 2005 despite a truce arranged and put into place by peace broker Norway in February 2002.