On the outskirts of the capital, tanks and troops combed through fields near the Barzeh neighborhood in the northeast as well as an area near Hamouriya in the east, activist Omar Hamzeh said via Skype.
"They are moving through the fields and firing anti-aircraft guns," he said, adding that the regime was probably looking to arrest activists. "The rural areas around there have been very active in protests against the regime."
The Observatory also reported army raids in Barzeh.
Activist claims could not be independently verified. The Syrian government prevents most media from working freely in the country.
World powers remain divided on how to stop Syria's crisis, though all have fallen in behind a plan put forward by former U.N. Secretary General Kofi Annan that seeks a cease-fire in order for all sides to engage in political dialogue.
But the truce that was to begin on April 12 has never really taken hold, with regime forces continuing to shell opposition areas and shoot at protesters. Security forces killed one teenager following a protests in the northern city of Aleppo on Friday.
Armed rebels have kept up attacks on military checkpoints and convoys.
A spokesman for Annan, however, said Friday the international envoy believes his peace plan for Syrian remains "on track" a day after the Obama administration offered a far bleaker view, saying the plan might be doomed.
A U.N. team of up to 300 members is to monitor compliance with the truce. U.N. peacekeeping chief Herve Ladsous said about 40 U.N. observers are on the ground in Syria and that the force will grow to 65 by Sunday.