"If not, we will immediately attack the hideouts of Assad's gangs and shabiha," added the man, who identified himself as Rashid Abul Fida, head of the Al-Ansar Brigade in Hama.
Syrian Observatory for Human Rights director Rami Abdel Rahman said the towns both had pre-war populations in the tens of thousands but that most of their residents have already fled.
As the news circulated, Syria's new Greek Orthodox leader called in Damascus for Christians to remain in the country despite the conflict.
Patriarch of Antioch and All the East Yuhanna X Yazigi also appealed to warring parties to renounce violence "in all its forms" and to start a process of dialogue.
In his first press conference since succeeding Ignatius IV Hazim, who died on December 5, he said: "We Christians are here in the country and we will stay here.
"We believe that Christ is always present in this region, which is where Christianity was born."
The patriarch sought to play down dangers faced by Christians.
"What is happening to us is happening to others too. We are in the same situation as everyone else, Muslims and Christians, shoulder to shoulder, facing the difficulties," he said.
There are some 1.8 million Christians in Syria.
Many have remained neutral in a conflict that erupted in March 2011 and has killed an estimated more than 44,000 people. Others, fearing a rise of Islamism, have taken Assad's side.
The messages came two days after UN investigators described the 21-month conflict as "overtly sectarian in nature."
In response, the opposition Syrian National Council, hit out against the UN Commission of Inquiry on Syria, saying the "revolution is neither sectarian nor bloody."
"The only division that Syrian society is witnessing is between a bloodthirsty, oppressive regime... and people calling for freedom and equality," said the SNC, whose chief George Sabra comes from a Christian background.
On Thursday, the commission said the conflict threatened whole communities, and warned that newly formed armed Islamist groups were increasingly operating independently of the main rebel force, the Free Syrian Army.
Fabrice Balanche, director of the French research centre Gremmo, says 80 percent of Syrians are Sunnis, around 10 percent belong to Assad’s Alawite community, five percent are Christian, three percent Druze and one percent Ismaili.
Meanwhile, there was no let-up of violence, as a car bomb in the northeast Damascus district of Qaboon killed five people, the Britain-based Observatory said.
And Haidar al-Sumudi, a cameraman for state television was gunned down outside his Damascus home, the broadcaster said.
Elsewhere, warplanes carried out air strikes on several flashpoints, among them the eastern province of Deir Ezzor and Homs in the centre of the strife-torn country, said the Observatory.
The Britain-based Observatory said at least 55 people were killed in violence across Syria on Saturday.
Despite Syria's raging war, Russian Foreign Minister Sergei Lavrov said he believed "no one has an appetite for external intervention" in the country's long-time ally.
"I even have the feeling that they are praying for Russia and China to continue blocking permission for external intervention. Because if there is such a decision, they will have to act, and no one is ready to act."
Lavrov also said Assad's regime is still in control of chemical weapons.
The United States said earlier this month it had intelligence showing that the regime was considering using its chemical weapons and issue a stark warning against any such action.