Suspected Tamil Tiger rebels killed five Sri Lankan soldiers in a second mine attack in the island's north in three days.
A recent surge in violence on the island has strained a 2002 truce between the Tigers and the government.
One officer and four regular soldiers were killed in the attack in the military held town of Jaffna, in Sri Lanka's far north.
Amnesty Secretary General Irene Khan
The attack comes after a separate claymore mine blast on Sunday killed seven soldiers in the deadliest attack since the ceasefire and brought the death 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 250 metres in a wide arc.
The government has blamed Sunday's attack on the Liberation Tigers of Tamil Eelam (LTTE), who last month threatened to resume their struggle for a separate homeland for ethnic Tamils next year unless given wide political powers.
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 result of flaring tensions between ethnic Tamils and Muslims.
Amnesty International yesterday 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.
"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 harrassment," Amnesty Secretary General Irene Khan said last night during a visit to Sri Lanka.
Nordic truce monitors have appealed to both sides to halt the violence, which is steadily eroding the ceasefire. More than 220 police, military, rebel cadres and civilians have now been killed since the truce was agreed, the monitors say.