(CNN) -- Guns mostly fell silent in Syria Thursday after an early morning cease-fire took effect and cast an eerie calm over restive cities and towns that had been pounded by government forces in recent days.
"Syria is apparently experiencing a rare moment of calm on the ground," said Kofi Annan, the special envoy who brokered Syria's peace plan.
"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."
Amid the fragile truce, opposition groups called for peaceful demonstrations, seemingly testing whether the government would stick to its word and the United Nations chief said the world was watching Syria with skepticism.
"Today marks a critical moment in our six-point plan for ending the violence in Syria," said U.N. Secretary-General Ban Ki-moon. "At this moment, the situation looks calmer. We are following it very closely."
Ban said he was working with the U.N. Security Council to send in international observers as promptly as possible.
"The onus is on the government of Syria to prove that their words will be matched by their deeds this time," Ban said at a news conference in Geneva. "The world is watching, however, with skeptical eyes since many promises previously made by the government of Syria have not been kept."
Anti-regime protesters came out onto the streets in several cities including Idlib, Homs, Deir Ezzor and Raqqa, according to the Local Coordination Committees (LCC), a network of opposition activists across Syria. It said troops opened fire at a checkpoint in Hama to prevent people from protesting.
Opposition activists reported sporadic violence and said President Bashar al-Assad had failed to pull back troops from population centers, another key condition of Annan's plan.
Adib al Shishakly, a member of the Syrian National Council, an umbrella group of exiles, said Damascus had not abided by all six points of Annan's peace plan.
"They diluted the whole initiative into one thing: into the cease-fire only," said al Shishakly. "What happened to the other five?"
Annan's plan also calls for the release of detainees, allowing access into the country for humanitarian aid and international media and respecting the rights of peaceful demonstrators.
The heavy troop presence meant that al-Assad's guns could be pointed back at people within a moment's notice and fears rose that large protests could spark violence.
At least seven people were killed Thursday, the LCC said. Among the dead were a child and two victims of sniper's bullets. The opposition group also reported resumed shelling in a neighborhood of Homs.
Syrian state-run television said an officer was killed Thursday and 24 others wounded in a terrorist bombing in Aleppo.
CNN is unable to independently verify reports of violence and deaths as the government has severely restricted access by international media.
But for the most part, after months of slaughter, residents of hotspots throughout the beleaguered nation woke up to the quietest day in months. The peace plan set a 6 a.m. deadline for a cessation of military action.
"Interestingly, we have been only hearing the sounds of birds," said Abu Salah, a Homs resident. "However, we have seen the security forces on alert."
Annan's plan, which appeared to falter in the days ahead of the deadline, is widely seen as the last chance for a diplomatic solution to the year-long crisis in Syria.
But many Syrians and international observers questioned whether al-Assad would adhere to the cease-fire, especially after the government made it clear that it reserved the right to fire back on aggressors.
The regime has reneged on previous promises to stop violence, and al-Assad has described anti-government rebels as armed terror groups spreading mayhem in the country.
"Armed terrorist ground escalate their criminal operations in an attempt to damage Syria's stability and Annan's plan," said a headline on Syrian state-run television.
Tanks were still roaming the streets, and snipers remained perched on rooftops in some cities, according to activists.
Opposition fighters stayed in some cities to ward off attacks by government forces, activists said.
"The Free Syrian Army members remain in Homs but there have been no clashes," activist Saif al-Arab said in reference to the army of military defectors. "They perceive their role as only to defend civilians in the face of any raids."
Just before the deadline, a tank fired mortar rounds into a residential area in Zabadani, 20 miles outside of Damascus, activists said.
"It was as if Assad's forces wanted to send a last message of warning," said Rania, a local activist who did not want to use a full name for safety reasons.
About seven hours into the deadline, the Syrian Observatory for Human Rights reported explosions and gunfire in Zabadani, Idlib, Homs and Bou Kamal.
Activists in Hama, Homs and Zabadani said there are no reports of detainees being released per Annan's mandate.
Syrian state media, SANA, reported that 106 men handed their weapons over to authorities in the Damascus and Lattakia areas, and pledged to return to normal life.
Ahead of the deadline Wednesday, a Syrian foreign ministry spokesman told CNN the government was "fully committed" to the peace plan, but said the opposition will also play a role.
"People should know that I can say optimistically that 40% of the keys to solve the crisis is in our hands as government," said spokesman Jihad Makdissi. "But the other 60% is in the hands of those who are harboring, channeling weapons, instigating in the media against Syria."
Opposition groups say deaths have occurred daily at the hands of al-Assad's forces. The day before the deadline, government forces attacked several cities, killing at least 98 people, the LCC reported.
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.