With a cease-fire in Syria teetering, Syrian forces widened their attacks on opposition strongholds on Tuesday as an advance team of international observers worked to broaden its mission in the country.

Rights groups and activists say at least two people were killed in violence on Tuesday. They say forces loyal to President Bashar al-Assad continued shelling in the central Homs region and in the northwestern Idlib province, in spite of a cease-fire that took effect five days ago.

The agreement, brokered by international envoy Kofi Annan, calls for government forces and the opposition to stop attacks. Mr. Annan is in Doha on Tuesday to brief the Arab League on Syria.

In Damascus, the head of an advance team of six unarmed United Nations observers said it would take time for monitors to reach the hardest hit areas. Moroccan Colonel Ahmed Himmiche said Tuesday the group's mission “is a difficult process [that] requires coordination and planning…we should move step by step.”

Middle East expert Nadim Shehadi tells VOA the monitors' presence will not curb violence in Syria unless the international community unites on a plan for the country.

“The monitoring mission will not be effective if there is no international will to support it and if there is no international coherent policy on Syria.”

U.N. chief Ban Ki-moon voiced concern on Tuesday that the size of the monitoring mission may be too small to have an impact. He said the total mission of about 250 monitors may not be enough “considering the current situation and the vastness of the country.”

Meanwhile, world powers are considering tighter economic pressure on Syria.

French Foreign Minister Alain Juppe says international economic sanctions have stripped Mr. Assad's government of half of its financial reserves. He commented on Tuesday at a meeting of officials from more 50 countries. The group met in Paris to coordinate sanctions against Syria.

In Moscow, Russian Foreign Minister Sergei Lavrov accused unspecified external forces of seeking to undermine Mr. Annan's efforts to end more than a year of bloodshed in Syria, saying support for government foes is threatening the fragile cease-fire.

In televised remarks Tuesday, Lavrov said such actors “are doing this by delivering arms to the Syrian opposition and stimulating the activity of rebels who continue to attack both government and civilian facilities.”

Russia has provided Syria's government with weapons and – along with China – shielded Mr. Assad by blocking U.N. Security Council resolutions condemning his government for a crackdown which the U.N. says has killed more than 9,000 people since March 2011.

Moscow has pledged its full support for Mr. Annan's peace plan and last week called on the Syrian government to step up implementation, but Russia has also put much of the blame for the bloodshed on opposition forces.