Smoke drifted over the skyline and explosions thundered throughout the besieged city, as long lines of civilians fleeing by car formed at checkpoints manned by revolutionary forces.
Anti-Gadhafi fighters pushed into the Mediterranean coastal city from the west, east and south in heavy fighting, trying to squeeze his supporters into a smaller and smaller perimeter. The two sides battered each other with rockets, mortar shells and tank fire, as Gadhafi snipers fired down on fighters advancing through housing complexes. Friday's push marked the largest new assault on the city in weeks. The former rebels had said they were delaying a final push to allow civilians to escape.
A U.S. administration official, speaking on condition of anonymity to discuss intelligence matters, said that 80 percent of the city was now pacified or under the control of the transitional government. The official said the remaining area might take a little more time as forces move methodically to eliminate the resistance.
NATO airstrikes have been critical to the rebels' successes. Fighters entering through the western gate on Friday quickly advanced to within just a mile (two kilometers) of the city center but faced heavy resistance from a loyalist force of roughly 800 men, according to one commander's estimate.
"We started the attack at 6 a.m. today. The first group hit the outskirts of Sirte. We were fired on by Gadhafi snipers. We had many soldiers wounded," said commander Altaib Aleroebi of the ex-rebels' West Mountain Brigade, which led the attack on the western front.
He said they then pushed into the city and targeted the Ouagadougou convention center, where Gadhafi's loyalists have been barricaded. From the grandiose conference hall, which Gadhafi built to host international summits, loyalist forces have been able to dominate the defense of surrounding residential areas.
The fighters moving toward the hall were driven back by heavy machine gun and sniper fire.
At least 12 revolutionary fighters were killed and 195 were wounded, doctors said. Ambulances sped down Sirte's main avenue to a field hospital set up in an abandoned villa five miles (eight kilometers) from the center. Doctors said a senior commander, Ali Saeh of the Free Libya Brigade, was injured, shot twice by a sniper as he led fighters through loyalist forces in a residential area.
"We are receiving many gunshot wounds, mostly to the head, neck and chest from sniper fire. We have received many injured today," Dr. Ahmed Mohammed Tantoun said Friday, adding he expects many more injured fighters to arrive through the day as fighting intensifies.
Sirte, Gadhafi's birthplace, is considered the most crucial of the areas that remain in the hands of supporters of the former Libyan leader. It is key to the physical unity of the oil-rich North African nation, since it lies roughly in the center of the coastal plain where the majority of Libya's 6 million people live, blocking the easiest routes between east and west.
Gadhafi loyalists still control Bani Walid in the central mountains, but the transitional leadership has said the landlocked city is not crucial to declaring liberation since it has no ports of entry to the country.
State Department spokeswoman Victoria Nuland said the U.S. trusted Libyan authorities to make that declaration at the right time.
"And I think that'll be a good thing to be able to move on to the next political and security steps, and effort to ensure that the country is united and that the reconciliation can also begin," she told reporters in Washington.
The international community has rallied around Libya's efforts to move forward with efforts to form a new government, with transitional leaders promising elections within eight months after liberation is declared.
British Defense Secretary Liam Fox and his Italian counterpart, Ignazio La Russa, arrived in Tripoli on Friday, the latest in a string of foreign dignitaries to visit the country.
Revolutionary fighters have faced grueling resistance as they encircled Sirte and besieged the city for some three weeks.
Deputy defense minister in the transitional government, Fawzi Bukatif, told The Associated Press called Friday's push a final attack on Sirte.
Fighting was also going on around a Gadhafi palace complex in the city and Green Square, the public plaza at the center of Sirte, between the convention center and the sea, commanders said.
As the attack continued, civilians fled the besieged city, which is suffering shortages of food, medical supplies and other essentials. Former rebel fighters checked the contents of their bags and cars.
"We had to go today ... there is nothing left, no food, no gasoline," said Sirte resident Ahmed Mohammed.
U.N. envoy Ian Martin appealed to both sides to respect human rights and look ahead to national reconciliation.
He urged the forces of Libya's new leaders not to take revenge on those accused of war crimes, saying they should be detained and brought to justice.
"This will lay the foundation for national reconciliation and the future unity of the people of Libya," he said.