More than 70 people have died since the first week of April in suspected rebel Tamil Tiger attacks, ethnic riots and other killings that have reignited fears of a return to the island's two-decade civil war.
In the latest violence, a claymore fragmentation mine blast in the northwestern region of Mannar injured two members of the Sri Lankan navy, the army said, adding that the attack could only have been carried out by the Liberation Tigers of Tamil Eelam (LTTE).
A Korean businessman was injured in a separate attack in the northern town of Vavuniya, his driver said.
The driver, 46-year-old Anura Nullaperuma, speculated that his vehicle had been mistaken for an army car.
"At first I thought a tyre had punctured. Then I saw all the windows and glass had shattered," he said.
The Tigers have denied involvement in recent mine attacks on troops, but few diplomats or analysts believe them.
The bodies of five Tamil men were found in the northern town of Jaffna, shot in the head, hospital officials said.
Residents blamed the army, but they denied any involvement.
A second round of talks in Switzerland had been due to start on Wednesday, but last week the Tigers said they could not attend, citing a dispute over the transport of eastern rebel commanders to a pre-talks meeting.
Norway, which brokered the island's strained 2002 ceasefire, has sent Jon Hanssen-Bauer, the special envoy, to secure talks and stop the violence.
Tamil Tigers said they could not
attend a second round of talks
Diplomats increasingly say neither side is serious and they are simply playing a political game.
Hanssen-Bauer did not get a meeting with Mahinda Rajapakse, the president, whose Marxist and Buddhist allies oppose any concessions to the mostly Hindu rebels, and instead only met the foreign minister on Wednesday in what some see as a snub.
"There's dissatisfaction with how things are being done," a government official said on condition of anonymity.
"Facilitation so far has meant just giving what the LTTE wants."
Hanssen-Bauer was also due to meet the Tigers on Thursday in Kilinochchi, their northern headquarters.
The Tigers pulled out of the talks after accusing the navy of monitoring too closely the transport of their eastern rebel leaders organised by the island's Nordic ceasefire monitoring mission.
The government eventually agreed to offer the use of a private helicopter, but a Tamil newspaper in Jaffna said the rebels looked set to turn down the offer, which the government says will only stand for another 72 hours.
Recent attacks reignite fears of
a return to the island's civil war
The Tigers have added new conditions for attending the Geneva talks, demanding a halt to attacks on Tamil civilians and labelling recent ethnic riots as genocide.
Analysts say they may not be ready for the compromises needed for a peaceful Sri Lanka, but that they are also angry the government has apparently done nothing to rein in breakaway former rebels, the Karuna group, which has been attacking the Tigers in the east.
Jehan Perera, director of the non-partisan National Peace Council, said: "They have not got what they want through peace and they think they are not going to get what they want, which is the disarming of Karuna.
"Using violence, they want the government to back down. But the government will not give up Karuna. They will not give up that advantage."