Libyan helicopter gunships strafed opposition fighters as forces loyal to Moammar Gadhafi pounded them with artillery and rockets Sunday, dramatically escalating a counteroffensive to halt the rapid advance of rebels toward the capital, Tripoli.

Another scene of heavy fighting was the city of Misrata, 120 miles (200 kilometers) east of Tripoli, where a doctor told The Associated Press 20 people were killed and 100 wounded. Residents said pro-Gadhafi troops punched into the city with mortars and tanks but were pushed out five hours later by rebel forces. The rebel commanders intentionally opened the way for government tanks to enter the city, then surrounded them and attacked with anti-aircraft guns and mortars, said Abdel Fatah al-Misrati, one of the rebels.

"Our spirits are high," he said. "The regime is struggling and what is happening is a desperate attempt to survive and crush the opposition. But the rebels are in control of the city," al-Misrati added.

With the counteroffensive intensifying, Libya sank deeper into chaos and heavy bloodshed while the international community appeared to be struggling to put military muscle behind its demands for Gadhafi to give up power. Britain said one of the most talked about ideas for intervention — the idea of a no-fly zone over Libya — is still in an early stage of planning and ruled out the use of ground forces.

"We call on the world to take action, to strike (Gadhafi's) powerful bases to rescue the civilians," one Misrata resident said. "He has all the power to smash the people."

Hundreds, perhaps thousands, have died since Libya's uprising began on Feb. 15, but tight restrictions on media make it near impossible to get an accurate tally. More than 200,000 people have fled the country, most of them foreign workers. The exodus is creating a humanitarian crisis across the border with Tunisia — another North African country in turmoil after an uprising in January that ousted its longtime leader.

Sunday's fighting appeared to signal the start of a new phase in the conflict, with Gadhafi's regime unleashing its air power on the poorly equipped and poorly organized rebel force trying to oust their ruler of 41 years. Resorting to heavy use of air power signaled the regime's concern that it needed to check the advance of the rebel force toward the city of Sirte — Gadhafi's hometown and stronghold.

If Sirte were to fall in rebel hands, it would give the anti-Gadhafi forces a massive morale boost and momentum that could carry them all the way to the gates of Tripoli.