One officer and six soldiers were killed in a Claymore mine attack on Tuesday in the town of Jaffna, in Sri Lanka's far north, on a peninsular hemmed in by a de facto separatist state.
The deaths in Jaffna, where the rebels operate, coincided with Sri Lanka's new hawkish military commander, Major-General Sarath Fonseka, taking over the country's armed forces, and could further strain the government's already fragile ceasefire with the separatists.
The soldiers "had done routine clearing operations of the area and were returning back on a tractor" when the landmine exploded, said army spokesman Brigadier Nalin Witharanagee.
The Tigers denied any hand in the blast.
Daya Master, the rebel media coordinator in Kilinochchi, said: "We are not involved. We are not going to break the ceasefire agreement."
Tuesday's attack comes after a separate landmine blast on Sunday killed seven soldiers in the deadliest attack since the ceasefire and brought the toll in a spate of attacks in the island's north and east to at least 19 since last week.
A Claymore is a fragmentation mine that sprays hundreds of small steel balls up to 250m in a wide arc.
The government blamed Sunday's attack on the Liberation Tigers of Tamil Eelam (LTTE), who last month threatened to resume its struggle for a separate homeland for ethnic Tamils next year unless given wide political powers.
Irene Khan (R): Human rights
have become a political weapon
The army has boosted troop numbers on the streets of Jaffna, where residents say the atmosphere is extremely tense.
Patrols have also been stepped up in the eastern port town of Trincomalee after two Tamil men were killed and three abducted Muslim farmers were found slain on Saturday.
Officials say the violence was the result of escalating tensions between Tamils and Muslims.
Human rights weapon
Amnesty International on Monday accused both the government and the Tigers of using human rights as a weapon by failing to probe the rash of killings, and called for an independent investigation body.
Irene Khan, Amnesty's Secretary-General, said: "It is a grave situation, volatile, ready to implode.
"It is a grave situation, volatile, ready to implode. We think it's very important that there be investigation that is independent and transparent and seen to be"
"We think it's very important that there be investigation that is independent and transparent and seen to be.
"Human rights have become a political weapon, where each side is trying to put the blame on the other side, and taking little concrete action to stop the spate of killings, abductions and harassment," she added.
Norwegian truce monitors have appealed to both sides to halt the violence, which is steadily eroding the ceasefire.
More than 220 police, soldiers, separatists and civilians have now been killed since the truce was made, the monitors say.