(CNN) -- The Syrian government has warned protesters in the city of Homs to stop demonstrations, hand in weapons and surrender defecting military members by Monday night or face bombardment, an opposition leader said.
A 72-hour warning was given Saturday, said Lt. Col. Mohamed Hamdo of the Free Syrian Army. Activists on the ground said the ultimatum was issued on Friday.
The Syrian National Council, the country's leading opposition movement, had warned earlier of a potential bloodbath at the hands of the Syrian regime in Homs.
"If the world continues to watch, then the massacre of Hama in the '80s will be repeated," said Hamdo, referring to 1982, when Syria's military -- acting under orders from current President Bashar al-Assad's father, Hafez al-Assad -- launched an assault on the city, killing thousands.
The military has dug trenches around Homs, Hamdo said.
"There is no electricity, water, or communication whatsoever now and the communication breakdown has extended even closer to the Turkish border," he said.
The Syrian government denied reports of water and electricity being out in the city, according to the state-run Syrian Arab News Agency (SANA).
The government made no mention of the reported deadline on the news agency's website Sunday morning.
Opposition figures launched a nationwide anti-government strike Sunday, which they called the "strike of dignity."
The London-based Syrian Observatory for Human Rights, which gets information from people in different parts of the country, said people in Homs and neighboring towns widely joined the strike. "All shops were closed on all main roads in the city," the group said.
Several videos posted on Youtube purported to show government loyalists breaking locks of shops that closed in support of Sunday's anti-government strike.
But on SANA, the Syrian government quoted people across the country as saying there was no strike and no sign of a strike. "It was a normal trading day in markets throughout the Syrian provinces as people bought and sold consumer goods, vegetables, fruit and clothes as economic elements shrugged off all inflammatory tendentious calls by terrorist groups that are associated with foreigners," the government insisted.
As violence raged Sunday in parts of the country, the death toll reached 23, according to the opposition Local Coordination Committees of Syria (LCC). Five of the dead were children, the group said.
The toll includes six people in Hama; six in Homs; five in Idlib; three in suburbs of Damascus, and three in Daraa, according to the LCC, a network of anti-regime activists in the country.
One of the deaths in the Daraa area took place in Jasem, where a man was arrested and then returned to his family dead after about three hours, the LCC said.
In the city of Aleppo, security forces burned down a factory in an industrial area that was participating in the strike, the LCC said.
SANA, meanwhile, reported that the "bodies of 13 martyrs from the army, security and police forces" were taken "to their final resting place." Four were from Homs.
Authorities in Homs arrested "armed men who tried to impose an obligatory sit-in" and who shot at people in cars and streets, SANA said.
CNN cannot independently confirm events because the Syrian government restricts access of international media to the country.
The Syrian government said authorities in Idlib "confronted members of an armed terrorist group" who were blocking a road and "killed and injured a number of its members." Authorities also chased another "armed gang" and killed two of its members, SANA said.
In Hama, Syria said, officials arrested "a member of armed terrorist groups" who was trying to plant an explosive device near residential buildings. SANA said the military dismantled the bomb and no one was injured.
Throughout the Syrian uprising, government officials have described some opposition fighters as armed terrorists and gang members.
There were clashes Saturday in Khan Sheikhon, where authorities "arrested a number of the terrorists and killed three of those groups' prominent leaders," SANA said in a report Sunday.
In the city of Kfar Takharim, "a number of the members of armed terrorist gangs were killed or injured in clashes with the authorities on Saturday evening," SANA said, adding that one member of the authorities was killed and six others were injured.
Fierce clashes were underway Sunday in the Daraa Province village of Busra al-Harir as Syrian troops battled defectors, leaving many people wounded, according to the Syrian Observatory for Human Rights.
Residents said members of Syria's 12th Armored Brigade, which is based near the border with Jordan, "stormed" Busra al-Harir. They said they heard explosions and heavy gunfire in the city and just north of it in Lujah, where defectors were believed to be hiding, the observatory said.
Security forces in Idlib were using mosque speakers to threaten residents to end their strike and to force people to reopen businesses, the observatory said, citing eyewitnesses.
The Arab League announced it will hold emergency meetings this week in Cairo. In a statement on Egypt's state-run MENA news agency, an Arab League official said leaders will "discuss the Arab response to a message from Syrian Foreign Minister Walid Moallem to approve the signing of an agreement on an Arab League observing mission to Syria with conditions."
World leaders have widely condemned Syria's crackdown and called on it to halt violence against the opposition.
On Saturday, France expressed its concerns about events in Syria, and warned against Syria launching a military operation against the city of Homs and its population, the French Foreign Ministry said in a statement.
Al-Assad's regime has denied targeting peaceful protesters.
The regime's actions have outraged world powers and sparked sanctions by the Arab League, Turkey, the United States and the European Union.
Israeli President Shimon Peres on Sunday described Syrian President al-Assad as a "killer," implicitly comparing him to Libya's ousted ruler Moammar Gadhafi.
"The world decided -- including the Arab world -- to intervene when a leader is beginning to kill his own citizens," Peres told CNN in an interview. "It happened in Libya; it's happening in Yemen; it's happening by the Arab League, for the first time in their experience. They decided to put pressure on an Arab state because the leader is killing his people."
The United Nations said this month that more than 4,000 people have died in Syria since the crackdown began in mid-March.
Protesters have been demanding the end of the al-Assad regime and democratic elections. Al-Assad has been in power since 2000; his father, Hafez, ruled Syria for three decades.
Local elections are set to take place Monday for municipal posts.
In its 2010 Human Rights Report about Syria, the U.S. State Department said Syria's elections have not been fair in the past.
"Although the constitution provides the right for citizens to peacefully change their government through elections, in practice they did not have that right because elections were neither free nor fair," the report said.
CNN's Amir Ahmed, Richard Quest, Josh Levs and Joe Sterling and journalist Mohamed Fadel Fahmy contributed to this report.