Tripoli, Libya ? Government forces in tanks rolled into the opposition-held city closest to Tripoli after blasting it with artillery and mortar fire, while rebels captured a key oil port and pushed toward Moammar Gadhafi’s hometown in a seesaw Saturday for both sides in the bloody battle for control of Libya.

With the Gadhafi regime’s tanks prowling the center of the city of Zawiya, west of Tripoli, residents ferried the wounded from the fierce fighting in private cars to a makeshift clinic in a mosque, fearing that any injured taken to the military-controlled hospital “will be killed for sure,” one rebel said after nightfall.

The rival successes — by Gadhafi’s forces in entering resistant Zawiya, and by the rebels in taking over the port of Ras Lanouf — signaled an increasingly long and violent battle that could last weeks or months and veered the country ever closer to civil war.

Rebels in the east advanced from their eastern stronghold toward Sirte, setting the stage for fierce fighting with pro-Gadhafi forces who hold sway in the tribal area.

Western leaders focused on humanitarian aid instead of military intervention, and the Italian naval vessel Libra left from Catania, Sicily, for the rebel-held port of Benghazi in eastern Libya, with 25 tons of emergency aid, including milk, rice, blankets, emergency generators, water purifying devices and tents. It is due to arrive early Monday.

The crisis in Libya has distinguished itself from the other uprisings sweeping the Arab world, with Gadhafi unleashing a violent crackdown against his political opponents, who themselves have taken up arms in their attempt to remove him from office after ruling the country for more than 41 years. Hundreds have been killed.

Gadhafi has drawn international condemnation for his actions. President Barack Obama has insisted that Gadhafi must leave and said Washington was considering a full range of options, including the imposition of a “no-fly” zone over Libya.

The storming of Zawiya, a city of some 200,000 people just 30 miles west of Tripoli, began with a surprise dawn attack by pro-Gadhafi forces firing mortar shells and machine guns.

“The number of people killed is so big. The number of the wounded is so big. The number of tanks that entered the city is big,” the rebel in Zawiya said, speaking on condition of anonymity because he feared government reprisal. The rebels vowed to keep up the fight in the city.

Witnesses who spoke to The Associated Press by telephone with gunfire and explosions in the background said the shelling damaged government buildings and homes. Several fires sent heavy black smoke over the city, and witnesses said snipers shot at anybody on the streets, including residents on balconies.

The rebels initially retreated to positions deeper in the city before they launched a counteroffensive in which they regained some ground, according to three residents and activists who spoke on condition of anonymity for fear of reprisals.

By midafternoon, the rebels had reoccupied central Martyrs’ Square while the pro-regime forces regrouped on the city’s fringes, sealing off the city’s entry and exit routes, the witnesses said. Members of the elite Khamis Brigade, named for one of Gadhafi’s sons who commands it, have been massed outside the city for days.

The pro-Gadhafi forces then blasted Zawiya with artillery and mortar fire in late afternoon before the tanks and troops on foot came in, firing at buildings and people, witnesses said.

Deputy Foreign Minister Khaled Qaid said “99 percent” of Zawiya is under government control.

The rebels fared better in the east, capturing the key oil port of Ras Lanouf on Friday night in their first military victory in a potentially long and arduous westward march.