Libyan army soldiers shout slogans against leader Moammar Gadhafi during a demonstration today in Tobruk, Libya. Heavy gunfire broke out in Tripoli as forces loyal to Gadhafi tightened their grip on the capital.

TOBRUK, Libya — Militiamen loyal to Moammar Gadhafi clamped down in Tripoli, with the sound of gunfire ringing in the air, while protesters who control much of the eastern half of Libya claimed new gains in cities and towns closer to the heart of Gadhafi’s regime in the capital.

Protesters said they had taken over Misrata, which would be the largest city in the western half in the country to fall into their hands. The military also has moved heavy forces into the town of Sabratha, west of the capital, to try to put down protesters who have overwhelmed security headquarters and government buildings, a news website close to the government reported.

International outrage mounted after Gadhafi on Tuesday went on state TV and in a fist-pounding speech called on his supporters to take to the streets to fight protesters. Gadhafi’s retaliation has already been the harshest in the Arab world to the wave of anti-government protests sweeping the Middle East.

Italy’s Foreign Minister Franco Frattini said estimates of some 1,000 people killed in the violence in Libya were “credible,” although he stressed information about casualties was incomplete. The New York-based Human Rights Watch has put the death toll at nearly 300, according to a partial count.

Gadhafi’s speech appeared to have brought out a heavy force of supporters and militiamen that largely prevented major protests in the capital Tuesday night or today. Through the night, gunfire was heard, said one woman who lives near downtown.

“Mercenaries are everywhere with weapons. You can’t open a window or door. Snipers hunt people,” she said. “We are under siege, at the mercy of a man who is not a Muslim.”

During the day today, more gunfire was heard near Gadhafi’s residence. The government sent out text messages urging people to go back to their jobs, aiming to show that life was returning to normal.

But Libya’s upheaval, just over a week old, has shattered the hold of Gadhafi’s regime across much of the country. Protesters claim to hold towns and cities along nearly the entire eastern half of the 1,000-mile Mediterranean coastline, from the Egyptian border. In parts, they have set up their own jury-rigged self-administrations.

At the Egyptian border, guards had fled, and local tribal elders have formed local committees to take their place. “Welcome to the new Libya,” a graffiti spray-painted at the crossing proclaimed. Fawzy Ignashy, a former soldier, now in civilian clothes at the border, said that early in the protests, some commanders ordered troops to fire on protesters, but then tribal leaders stepped in and ordered them to stop.

“They did because they were from here. So the officers fled,” he said.

Protesters have claimed control all the way to the city of Ajdabiya, about 480 miles east of Tripoli, encroaching on the key oil fields around the Gulf of Sidra.

That has left Gadhafi’s power centered around Tripoli, in the far west and parts of the country’s center. But that appeared to be weakening in parts.

Protesters in Misrata were claiming victory after several days of fighting with Gadhafi loyalists in the city, about 120 miles east of Tripoli.

Residents were honking horns in celebration and raising the pre-Gadhafi flags of the Libyan monarchy, said Faraj al-Misrati, a local doctor. He said six people had been killed and 200 wounded in clashes that began Feb. 18 and eventually drove out pro-Gadhafi militiamen.

Residents had formed committees to clean the streets, protect the city and treat the injured, he said. “The solidarity among the people here is amazing, even the disabled are helping out.”

The division of the country — and defection of some army units to the protesters — raises the possibility the opposition could try an assault on the capital. On the Internet, there were calls by protesters for all policemen, armed forces and youth to march to Tripoli on Friday.

In his speech Tuesday night, Gadhafi defiantly vowed to fight to his “last drop of blood” and roared at supporters to strike back against Libyan protesters to defend his embattled regime.