(CNN) -- Syrian forces targeted opposition neighborhoods Saturday, activists said, days into a fragile cease-fire aimed at ending a bloody crackdown against anti-government protesters.
In escalated attacks, government troops opened fire on protesters in Daraa, injuring at least 20, the London-based Syrian Observatory for Human Rights said.
Regime forces also raided homes in the area and arrested five people, according to the opposition group.
In the flashpoint city of Homs, forces shelled neighborhoods at dawn for one hour, the group said. In a separate incident, a resident was killed and two others injured when a car exploded after an attack by forces.
The attacks come a day after protesters poured onto the streets, seemingly testing whether President Bashar al-Assad would stick to a provision in a six-point peace plan implemented by international special envoy Kofi Annan that allows peaceful demonstrations.
The cease-fire, which is part of the peace plan, went into effect at dawn Thursday.
The cease-fire is part of the Annan plan that includes the release of detainees, allowing access for humanitarian aid and international media, and respecting the rights of peaceful demonstrators. The plan also calls for the withdrawal of troops and heavy weapons from residential areas.
However, Syria is not in full compliance with the peace plan, and troops and heavy weapons remain in population centers despite an agreement to withdraw, said Susan Rice, the U.S. ambassador to the United Nations.
"We are worried about the operational deployment of heavy armor in population centers," said Ahmad Fawzi, Annan's spokesman. "They do not belong there. And we are working with the government and with the opposition for a full cessation of violence in all its forms."
The spokesman said the clashes are not over yet.
"We are under no illusion that we have come to the end of this conflict," Fawzi said. "This is only the beginning of a long road towards reconciling and towards building the future that Syrians aspire to."
As the international community keeps an eye on the truce, talk of the need for international observers increased.
The Security Council may vote soon on a draft resolution that demands Syria to allow the deployment of up to 30 international observers and allow them unimpeded freedom of movement. The draft also calls on all parties to cease armed violence. A vote was not expected late Friday.
Bashar Jaafari, Syria's ambassador to the United Nations, said the government would have to approve such a deployment.
Syria's anti-government protests erupted in March 2011, followed by a bloody government crackdown. The United Nations estimates at least 9,000 people have died in Syria since the protests began. The Local Coordination Committees of Syria puts the death toll at more than 11,000.