More than 200 people are known to have died, doctors say, with 900 injured.
The most bloody attacks were reported over the weekend, when a funeral procession is said to have come under machine-gun and heavy weapons fire.
One doctor, saying that fresh gunfire had broken out, told the BBC that what had happened was "a real massacre".
Human Rights Watch says at least 173 people have been killed in Libya since demonstrations began on Wednesday. Benghazi, the country's second city, has been a leading focus of protests against Col Muammar Gaddafi's rule.
Libya is one of several countries in the region to have seen pro-democracy campaigns since the fall of long-time Tunisian President Zine El Abidine Ben Ali in January. Egypt's Hosni Mubarak was forced from power on 11 February.
The current unrest in Libya is the most serious challenge to Col Gaddafi in his four decades in power.