Donors ask Lanka to honour truce

The United States, Japan, the European Union and Norway, heading efforts to drum up international support for the peace process, said in a joint statement they were alarmed by the deteriorating situation and the 2002 truce.

"Unless security is guaranteed, a central pillar of the ceasefire agreement will be undermined," the statement said.

"If the ceasefire agreement ceases to function, the wider peace process would be gravely jeopardised and international support for that process would be deeply eroded."

The warning from the peace effort's co-chairs came as Sri Lanka, trying to ease tension in the volatile northeast coastal region, stepped up a probe into charges that security forces were involved in the killing of four Tamil rebels earlier this month.

President Chandrika Kumaratu-nga's spokesman said she had ordered a broad investigation to identify those responsible for the deaths of the unarmed rebels, which sparked a wave of bombings in the region.