Syria's state television says 120 members of the security force have been killed in the northern town of Jisr al-Shughour in an ambush by "armed groups".
The report on Monday said that security forces were on their way to the town in response to calls for help from residents, and they died in an ambush and an explosion at a post office.
"The armed groups are using weapons and grenades ... the people in Jisr al-Shughour are urging the army to intervene speedily," state TV said.
Speaking to Al Jazeera, Reem Haddad, Syria's information ministry spokesperson, said "this afternoon 40 security officers were killed, and 80 have died since Friday".
The international media is banned from covering the uprising in Syria, making it nearly impossible to verify the state-controlled media's claims.
In reaction to the reported deaths, Mohammed Ibrahim al-Shaar, the Syrian interior minister, warned that Syria would hit back at armed groups.
"The state will act firmly, with force and in line with the law. It will not stay arms folded in the face of armed attacks on the security of the homeland," he said in a statement read on television.
However, an activist in Jisr al-Shughour, who spoke to Al Jazeera on condition of anonymity, said that the situation in the city was "quiet" on Monday after the previous day's violence.
"Today we didn't have any particular events, the situation was calm. But we had some news that there was a group of armed forces headed towards us," he said.
"The Syrian television is always against the street. If we have hundreds of demonstrators, the Syrian TV will say dozens. There is a big gap between the media in Syria and what is happening in the street."
"I think the regime has for the past weeks been trying to turn this into a sectarian war."
Middle East analyst
Syrian security forces have been conducting military operations in Jisr al-Shughour for several days as part of a crackdown on anti-government protests.
"The area there has been witnessing many clashes for the past few days," Al Jazeera's Rula Amin reported from Beirut in Lebanon.
"It is very difficult to verify the two different versions of these events.
"The official version of what is happening is that there are armed groups roaming the area ... that army and the security forces are facing hundreds of armed gangs, and this is a large number. Obviously the protests and confrontation between the protesters and the security police has taken a new turn."
"From the activists and the protesters, we know they have been keen on emphasising the protests are peaceful."
Our correspondent said over the past two days "we have seen on Facebook and Twitter debates even within those activists and opposition figures on the new phenomenon of some of the protesters resorting to arms, attacking the security forces, sometimes with weapons".
An activist told Reuters that police and members of the security forces in Jisr al-Shughour were killed by gunmen.
"Some people in some areas have taken up arms," he said. "The situation is grave, what is happening is an armed rebellion. I oppose violence from whatever side it comes from."
Fares Braizat, a Middle East analyst, told Al Jazeera there was a "war of pictures and a war of the media" going on in Syria.
"Now the only available version for viewers in Syria and outside Syria is the official version coming from Syrian TV or the Syrian official state agency," he said.
He said that following a massacre that took place in the Jisr al-Shughour area in the 1980s, "the people of this area have a longstanding revenge that they want to take out against the Syrian regime.
"So if violence escalates to unprecedented levels ... I think this is where the regime wants the process to be. I think the regime has for the past weeks been trying to turn this into a sectarian war."
In another development on Monday, violence broke out in a Palestinian refugee camp in Damascus, a day after Israeli troops shot dead protesters at a pro-Palestinian rally at the Syrian-Israeli border.
Six people were reportedly killed when a funeral for some of the victims in the Yarmouk camp turned violent.
Mourners accused the Popular Front for the liberation of Palestine (PFLP), the group organising the protest, of inciting young people to put themselves in the firing line. The headquarters of the group in Yarmouk was burnt down.
Syrian state television said 23 demonstrators were killed by Israeli forces during the rally at the Golan Heights ceasefire line, while Israel's military said it counted 10 protesters dead - none of whom was killed by Israeli fire.
Rights groups say more than 1,100 civilians have been killed and at least 10,000 arrested in Syria since protests against Bashar al-Assad's rule erupted in mid-March.
The Syrian government insists the unrest is the work of "armed terrorist gangs" backed by Islamists and foreign agitators.
Six human-rights groups within the country issued a joint statement on Monday condemning "the excessive use of force to disperse peaceful gatherings of unarmed Syrian citizens".
They also demanded an independent and transparent commission of inquiry "to unmask those responsible for the violence".
Source: Al Jazeera and agencies