Syrian troops on Monday fought street battles with rebels in suburbs of the capital, Damascus, as the government tries to push back a rebellion that has reached its doorstep, dpa reported.
Video posted on YouTube by activists showed black smoke rising from the eastern suburb of Ghouta, where large numbers of tanks and troops were deployed. Government forces also bombarded the eastern area of Saqba, which was controlled by rebels at the weekend.
The flare-up comes as the United Nations Security Council prepares to debate the Syrian crisis this week, with the Arab League expected to submit a report on the violence to the international body.
Russia, which is opposed to any Security Council draft resolution that calls on President Bashar al-Assad to step down, on Monday invited the Syrian government to hold talks with the opposition in Moscow to end the violence.
It remains unclear if the opposition has accepted the offer. Opposition groups have in the past criticized the Kremlin for its backing of the government and its veto at the Security Council in October of a resolution threatening al-Assad with sanctions.
An Arab diplomatic source told dpa that Arab League chief Nabil al-Arabi was trying to persuade Russia and China, Security Council members and Syria allies, to support an Arab-Western plan that calls on al-Assad to step down and hand power to his vice-president.
The escalating violence, which on Monday left 42 people dead, will add urgency to the UN debate this week.
"We lost 27 martyrs in fierce battles in Ghouta," Abu Ahmed al-Hamzawi, a member of the rebel Free Syrian army, told dpa by phone from Damascus. "They will pay a high for their massacres."
The head of the London-based Syrian observatory for Human Rights, Rami Abdul Rahman, told dpa that six government troops and three civilians in the southwestern city of Daraa, near the border with Jordan.
The state-run news agency SANA blamed a "terrorist group" for an attack on a gas pipeline near the border with Lebanon, which was often targeted in the uprising that erupted in March 2011.
The opposition Syrian Association for the Defense of Human Rights said on Monday that government soldiers executed senior army dissident Colonel Hussein Harmoush by firing squad.
Harmoush, who joined the Free Syrian Army in June and had a major role in its formation, was reportedly captured at his hideout in Turkey in September by secret agents loyal al-Assad.
He then appeared on state television on September 20 denying that he had defected and that he was never ordered to fire at civilians.