(CNN) -- Helicopter gunships fired on civilians Wednesday in the besieged neighborhood of Baba Amr as Syria's intensifying campaign triggered fears among residents that a full-fledged ground invasion could be imminent, opposition activists said.
Baba Amr, in the opposition stronghold of Homs, was also under its heaviest shelling yet and ground troops advanced in al Hakura, in the old part of the neighborhood.
While helicopters have flown over the area in previous days, Wednesday marked the first time they fired at people on the ground, two opposition activists in Baba Amr said.
Violent clashes between the regime's army and the opposition's Free Syrian Army lasted hours, opposition activists said.
Numerous neighborhoods in Homs were under violent attacks and explosions that shook the area, including al Khalidiya, al Bayada, Karm al Zaytoun, Bab Sbaa and others, an opposition activist said.
There was a water, electricity, and communications outage and a crippling blockade by the regime's battalions on the neighborhoods, the activist said.
France said it was trying to evacuate its two nationals stranded in Homs, in coordination with Syrian authorities and the Red Crescent. "We expect the government of Damascus to meet all the conditions for a safe and rapid evacuation, including an immediate cease-fire on Baba Amr," French Foreign Ministry spokesman Bernard Valero told CNN.
Syrian state-run news agency SANA, which consistently blames the violence on "armed terrorist groups" reported on violence in Homs as well. One such "terrorist group" killed a nurse at a hospital, while another attacked a water plant in the Homs countryside, SANA said.
Violence also raged in other parts of the country.
A 13-year-old boy was killed by sniper fire in the eastern city of Deir Ezzor, said the Syrian Observatory for Human Rights, an opposition activist group.
And an undisclosed number of people were killed and injured by rockets falling on the western city of Rastan, the group said.
Meanwhile, in the Damascus suburb of Zabadani, Syrian forces stormed residential buildings searching for and detaining men ages 13 and above, said an opposition activist named Mostapha.
CNN and other media outlets cannot independently verify opposition or government reports because Syria has severely limited access to the country by foreign journalists. But the vast majority of reports from the ground indicate that government forces are killing citizens in an attempt to eliminate those seeking President Bashar al-Assad's ouster.