Norwegian truce monitors are preparing to end their mission in Sri Lanka after the government formally withdrew from a repeatedly violated cease-fire deal with Tamil Tiger rebels.

Foreign Minister Rohitha Bogollagama told reporters Friday that Norwegian monitors will have what he call a redefined role - but he did not elaborate.

On Thursday, the Sri Lankan government notified the mission of its decision to pull out of the 2002 Norwegian-brokered truce, saying the agreement had allowed Tamil rebels to regroup and rearm. Colombo considers the rebels - drawn from the nation's minority ethnic Tamils - terrorists but says it remains committed to a political solution.

Meanwhile, Human Rights Watch called on the United Nations to send observers to help protect civilians after the Nordic monitors withdraw.

Elaine Pearson, deputy Asia director with the group, said while the Norwegian mission was deeply flawed, it helped minimize abuses against civilians caught in the escalation of the conflict. She said the need for a U.N. mission is now greater than ever.

The collapse of the truce was accompanied by continued battles near rebel-held territory in Sri Lanka's north and alarm in the international community.

U.N. Secretary-General Ban Ki-moon said he is deeply concerned about the government's decision. He urged all sides to protect civilians and the delivery of humanitarian aid to affected areas.

The U.S. State Department also said it is troubled by the termination of the cease-fire and called on both sides to find a peaceful political settlement to the violence.

Sri Lankan rebels have been fighting since 1983 to create a separate homeland for minority Tamils, claiming discrimination from the Sinhalese majority. Some 70,000 people have been killed.

Some information for this report was provided by AFP and AP.