Yangon (dpa) – Four ethnic rebel groups and a student militia in Myanmar said on Tuesday that they were prepared to sign a national ceasefire agreement after four years of negotiations.

They were the first to respond to a letter sent by President Thein Sein last week to 15 armed groups, urging them to sign the truce as a first step ahead of political dialogue.

Government and rebel representatives are scheduled to meet August 25 to finalize details of the ceasefire, officials said. Talks have hit an impasse over how many of Myanmar's rebel groups to be included.

The government list of 15 excludes six other groups still actively fighting the military in the eastern state of Shan. The rebels have demanded that at least two of those be included, bringing the total in the talks to 17.

Tuesday's joint statement by the ethnic groups was signed by the Karen National Union (KNU), the Democratic Karen Buddhist Army, the Karen National Liberation Army -Peace Council, and the Restoration Council of Shan State/Shan State Army group.

The All Burmese Students Democratic Front issued its own statement of willingness to sign the ceasefire.