Maoist rebels in Nepal say they are declaring a one-month cease-fire. Nepal's prime minister says he is suspicious of the offer, and the Maoists cannot be trusted.

In a faxed statement to news agencies, the Maoist leader, known as Prachand, said a cease-fire would begin on May 15 and continue until mid-June. The statement also said the Maoists would resume fighting if government troops attacked them.

Speaking in the United States where he is on an official visit, Nepal's Prime Minister Sher Badhadur Deuba told the Cable News Network the cease-fire offer would be suspect unless the Maoists laid down their arms and renounced violence.

Government forces say they have killed hundreds of rebels in an offensive in the Maoist stronghold of western Nepal over the past few days. The Maoists struck back on Wednesday, taking over a government base and allegedly killing more than 100 troops.

Reports of casualties cannot be independently confirmed.

The fighting took place as Nepal's prime minister held talks with President Bush getting pledges of more aid to fight the rebels. U.S. officials have already pledged $20 million in non-lethal military assistance to Nepal.

A U.S. military assistance team recently completed a visit to Kathmandu, to conduct an in-depth review of Nepalese military capabilities.

The Maoists who are fighting to overturn the world's only Hindu kingdom, have declared cease-fires on two previous occasions. Last November they resumed fighting after holding three rounds of talks with government officials. The move prompted Nepal's King Gyanendra to authorize a state of emergency which allowed Nepal's Army to join the fight against the Maoists.

Since then, fighting has intensified with more than 2,000 deaths reported, which is half the number killed in the six-year insurgency. Maoist leaders offered to resume peace talks last week, but the offer was rejected by Prime Minister Deuba, who says the Maoists must surrender their arms before any talks can begin.