JAFFNA, Sri Lanka -- Senior U.S. officials headed for Sri Lanka's Jaffna peninsula on Friday to throw Washington's weight behind Prime Minster Ranil Wickremesinghe's peace mission to the epicenter of the island's ethnic war.

The visit by Assistant Secretary of State for South Asia Christina Rocca and marine Brigadier General Timothy Ghormley will underline the carrot-and-stick diplomacy that helped Norway broker a truce between the government and Tamil guerrillas, AFP reported.

Earlier this week, Washington warned the rebel Liberation Tigers of Tamil Eelam (LTTE) against reneging on the truce and the U.S. embassy said on Friday that Deputy Secretary of State Richard Armitage had assured Norway of America's support.

"The government of Sri Lanka and the LTTE need to grasp this opportunity to end Sri Lanka's tragic conflict," Armitage was quoted as telling Norway's Deputy Foreign Minister Vidar Helgesen in Washington on Thursday.

Rocca, the highest ranking U.S. diplomat to visit Jaffna, will hold talks with Wickremesinghe, who received a rapturous welcome on Thursday when he became the first prime minister in 20 years to tour the heartland of the island's Tamil minority.

Jaffna was once part of a defacto state run by the rebels who have used a massive suicide squad to spearhead their campaign for a separate Tamil state in Sri Lanka's north and east.

The rebels are listed as a terrorist group by several Western countries including the United States, which threatened on Monday to tighten the noose around the guerrillas if they tried to undermine the truce.

The rebels, whose finances depend on an international Tamil Diaspora, immediately promised to fall in line -- a rare public acknowledgement of the intense diplomatic pressure on both sides to end a conflict that has killed more than 64,000 people.