Syria's two leading opposition groups have agreed on the ground rules for what they call "a transitional period" after the end of the regime of President Bashar Assad, activists said Saturday.

Representatives from the Syrian National Council (SNC) and the National Coordination Body for Democratic Change in Syria signed the agreement in Cairo late Friday after talks that lasted more than a month, activists said.

The accord is to be presented as an official document to the Cairo-based Arab League on Sunday, reported the independent news site Syria Politic.

There was no immediate comment from the pan-Arab organization.

Under the agreement, a new constitution is to be drafted for post-Assad Syria "guaranteeing the creation of a civil multi-party parliamentary system."

It envisages a one-year transitional period starting with an interim government taking over in Syria until a new constitution is approved.

The agreement recognizes the Kurdish minority as "an essential and historical part" of Syria. Kurds make up about 9 per cent of Syria's population and have long complained about government discrimination.

Martin Nesirky, spokesman for Secretary-General Ban Ki-Moon, said Friday that the league efforts to peacefully resolve the crisis in Syria are important.

Meanwhile, Arab League peace observers, who are inspecting hotspots across the country, have called on the government to "immediately" remove snipers from rooftops of buildings, a source close to the delegation told DPA on Saturday.

"The observers saw the snipers with their own eyes in Douma," the source said, referring to a restive town on the outskirts of the capital Damascus.

Footage posted on the internet showed observers spotting snipers also in the two provinces of Daraa and Idlib.

The monitors are in Syria to verify the government's compliance with an Arab peace plan, which includes removing military hardware from Syrian cities and the freeing of political prisoners.

Martin Nesirky, spokesman for United Nations Secretary-General Ban Ki-Moon, said Friday that the league efforts to peacefully resolve the crisis in Syria are important.

Nesirky called on the Syrian government to give the Arab League's observer mission unhindered access and its full cooperation.

Activists in Idlib, near the Syrian-Turkish border, said the Syrian army had hidden tanks as a team of observers was inspecting the province.

"They pulled the tanks from the main streets as the team was passing by the area. They brought them back after the monitors left," Omar Idlibi, a Syrian activist, told DPA.

"This regime is maneuvering to cover up realities on the ground," Idlibi added.

Meanwhile, a mass funeral was held Saturday for three civilians allegedly killed by security forces in Idlib the day before, reported the opposition Syrian Observatory for Human Rights.

The mourners chanted anti-government slogans and vowed revenge, added the London-based watchdog.

The ongoing violence in Syria, and new questions about the human rights record of the head of the Arab League monitors, are reinforcing the opposition's view that Syria's limited cooperation with the observers is nothing more than a ploy by President Bashar Assad's regime to buy time and forestall more international condemnation and sanctions.

There is broad concern about whether Arab League member states, with some of the world's poorest human rights records, were fit for the mission to monitor compliance with a plan to end to the crackdown on political opponents by security forces. The United Nations says some 5,000 people have been killed in the government campaign since March.

One of Assad's few remain allies, Russia, voiced its approval of the observer mission so far, saying the situation was "reassuring." At the same time, a group of dissident soldiers who joined the opposition announced it has halted attacks on regime troops since the observers arrived in a bid to avoid fueling government claims that it is facing armed "terrorists" rather than peaceful protesters.