The Sri Lankan military says at least six soldiers have been killed in a landmine explosion in the northern city of Jaffna.

Officials said the blast occurred when the troops were on a patrol in the Tamil city early Tuesday morning.

The attack came two days after nine soldiers were killed in Jaffna peninsula - seven in a landmine blast and two in other incidents of violence.

The military has accused the Tamil Tiger rebels of trying to provoke the army and create a volatile situation.

The United States has condemned the upsurge of violence in Sri Lanka. A State Department statement Monday called on the Colombo government and Tamil Tiger rebels to uphold the terms of the February 2002 ceasefire agreement.

The Sri Lankan government says the violence show the rebels are not sincere about reaching a political settlement.

Rebel leader V. Prabhakaran has threatened to step up his struggle for a Tamil homeland next year if the two sides fail to reach a settlement.

Some information for this report provided by AP and AFP.