(CNN) -- Syrians poured into the streets after Friday prayers, chanting and raising opposition flags in a major test of a fragile cease-fire implemented a day earlier to end a bloody government crackdown.
"God, we have no one to ask for help but you," they chanted. "Down with Assad!"
The opposition called for protests, seemingly testing whether President Bashar al-Assad would stick to a provision in a six-point peace plan that allows peaceful demonstrations.
Heavy security remained in the capital of Damascus and elsewhere, including Hama province and farther south in Homs, opposition activists said. Snipers remained perched on roofs in some towns, they said.
"It is a normal day like any other day. The troops have not withdrawn at all. Two of my relatives and friends were arrested," said Tariq, an activist just outside the city of Homs, whose name was withheld for security reasons. "The protests are peaceful, but there is still shelling and we are still under siege."
The rallies came amid reports that Syrian troops had clashed with defecting soldiers near the Turkish border in a violation of the cease-fire, the Syrian Observatory for Human Rights said. The border clashes occurred in Kherbet Joz village.
"In the incident, military forces moved in as part of an operation to attack one of the areas where defecting militants were based," the opposition group said. "Initially, the militant group tried to avoid clashing with the security forces, so it withdrew. But later, clashes did erupt and lasted for a few minutes."
The state-run SANA news agency reported that an "an infiltration attempt from Turkey to Syria by an armed terrorist group was thwarted."
Elsewhere in Syria, clashes left at least 13 people dead Friday, according to the opposition Local Coordination Committees (LCC) of Syria. The deaths occurred in Hama, Daraa, Hasaka and Idlib provinces.
The Syrian Observatory for Human Rights reported that a Hama death was a protester killed by security forces gunfire as he headed to a main square to join other demonstrators.
As it has in the past, the government blamed "terrorist groups" for the violence.
SANA also reported that an "armed terrorist group" killed an officer in Hama and that a law enforcement officer was killed by the same type of group in Aleppo.
These groups and their supporters aim to derail the peace plan, the news agency reported.
CNN is unable to independently verify reports of violence and deaths as the government has severely restricted access by international media.
Both sides have reported scattered violence since the cease-fire was implemented at dawn Thursday. The world turned a skeptical eye toward Syria after the truce cast relative calm over cities and towns previously pounded by government forces.
"Syria is apparently experiencing a rare moment of calm on the ground," Kofi Annan, the special international envoy who brokered the peace plan, said at the time. "This is bringing much-needed relief and hope to the Syrian people who have suffered so much for so long in this brutal conflict. This must now be sustained."
The cease-fire is part of a six-point 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. We are thankful that there is no heavy shelling; that the number of casualties is dropping and the number of refugees crossing the border is also dropping.
"We are under no illusion that we have come to the end of this conflict. This is only the beginning of a long road towards reconciling and towards building the future that Syrians aspire to."
Damascus needs to abide by all six points of Annan's peace plan, said Adib al Shishakly, a member of the Syrian National Council, an umbrella group of exiles.
"They diluted the whole initiative into one thing: into the cease-fire only," al Shishakly said. "What happened to the other five?"
Foreign ministers from the Group of Eight, or G8, welcomed the "fragile cessation of violence" during a meeting in Washington on Thursday.
"The ministers support the steps outlined by the special envoy and call for urgent action by the U.N .Security Council to follow through on those steps, including the immediate approval of an advance observer mission," the ministers said in a statement.
The G8 comprises Canada, France, Germany, Italy, Japan, Russia, the United Kingdom and the United States.
The United States is providing the opposition with nonlethal specialized equipment.
President Barack Obama recently signed off on the aid, which according to two senior officials, includes medical supplies and communications equipment, plus hardware and software to avoid being detected by the regime. Still under consideration and debated, according to the officials, are night-vision goggles, bulletproof vests and other equipment.
Key countries may meet next week in Paris to discuss the crisis, diplomatic sources said.
The sources said the meeting is not a done deal, but is likely and could prove timely because the situation inside Syria could change significantly in the coming week.
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 LCC puts the death toll at more than 11,000.
CNN's Amir Ahmed, Elise Labbott and Moni Basu contributed to this report.