GENEVA (Reuters) - An initial team of U.N. ceasefire monitors is due to arrive in Syria on Sunday evening and will be deployed on Monday, the spokesman for international mediator Kofi Annan said.

They will be joined by at least two dozen more in coming days in line with a U.N. Security Council resolution adopted on Saturday authorizing their deployment, Ahmad Fawzi said.

"The first batch of six U.N. observers arrives tonight, they will be on the ground in blue helmets tomorrow (Monday)," Fawzi told Reuters in Geneva.

The six, who include a Moroccan colonel leading the unarmed team, will arrive from New York, he added.

"They will be quickly augmented by up to 25 to 30 from the region and elsewhere," Fawzi said.

Syrian government forces shelled the city of Homs on Sunday, resident opposition activists and a rights activist said, as the six-person advance party of U.N. observers was due to arrive in Syria to monitor a ceasefire meant to start four days ago.

U.N. Secretary-General Ban Ki-moon, in remarks made in Geneva on Saturday night, said he would make proposals by next Wednesday regarding the full observer mission, expected to number about 250.

"The Security Council will adopt the next resolution authorizing deployment of the full mission based on report from the Secretary-General next week," Fawzi said on Sunday.

(Reporting by Stephanie Nebehay; Editing by Jon Hemming)