TRIPOLI, Libya – Libyan fighters came under heavy fire from rockets, machine guns and snipers Friday as they tried to push into two key strongholds of former leader Moammar Gadhafi in a concerted attempt to crush resistance by his loyalists.

In one of those areas, Bani Walid, the anti-Gadhafi forces had retreated by the end of the day.

Turkish Prime Minister Recep Tayyip Erdogan flew into Tripoli to meet the new government, stopping for Friday prayers and to address a small crowd in the the city’s central Martyrs’ Square.

Erdogan joined in calls for Gadhafi and his supporters to lay down their arms and warned the “oppressors” in Syria that they also would not survive.

Anti-Gadhafi forces had moved cautiously against the bastions of the former regime since taking Tripoli last month, keen to avoid civilian casualties and concerned about the resistance they might face. But on Friday, they appeared to have decided the time for waiting was over.

“It is a concentrated effort,” said Transitional National Council spokesman Jalal el-Gallal. “The intensity will only increase.”

In Gadhafi’s hometown of Sirte, a key prize in the Libyan conflict, Gallal said revolutionary forces now control the airfield and residential areas on the outskirts.

Fierce battles raged along one of the main boulevards leading into Sirte as black clouds of smoke rose from the city. Pickup trucks mounted with heavy machine guns roared past checkpoints on their way to the city, where the green flags of Gadhafi’s government still flew from mosques and other buildings.

Anti-Gadhafi fighters also initially appeared to make progress in their advance on the desert oasis town of Bani Walid, about 100 miles southeast of Tripoli, occupying a military headquarters on the northern outskirts and aiming mortar shells toward the central square.

Inside the town, a loyalist radio station kept up a steady stream of invective against the revolutionaries and called on residents to join the fight.

“Run from Bani Walid and you run straight to your graves,” shouted one announcer. Another claimed that the revolutionaries were trampling Muslim values.

“These revolutionaries are fighting to drink and do drugs all the time and be like the West, dance all night,” he said. “We are a traditional tribal society that refuses such things and must fight it.”

Revolutionary forces have also advanced steadily through the desert this week toward Sabha, a Gadhafi stronghold about 480 miles south of Tripoli, and are now in control of the Wadi al-Shati valley and the town of Birak, 50 miles north of Sabha, witnesses said.

In Tripoli, Erdogan urged the people of Sirte to join the movement for democracy in Libya, and he stepped up his rhetoric against the rule of Syrian President Bashar al-Assad.

His comments echoed those of French President Nicolas Sarkozy and British Prime Minister David Cameron in Libya on Thursday, saying Libya’s example gave hope to those fighting oppression in Syria.

“You are the ones who showed the whole world that no administration can stand in the way of the might and will of the people,” Erdogan told a cheering crowd in Tripoli.

“Do not forget this: Those in Syria who inflict repression on the people will not be able to stand on their feet.”