MOGADISHU, Somalia - Insurgents shot an Ethiopian helicopter gunship out of the sky Friday and mortar shells slammed into a hospital during the worst fighting in the capital in more than 15 years, leaving corpses in the streets and wounding hundreds of civilians.

At least 30 people, and likely many more, have been killed since Thursday.

The violence came on the second day of an offensive in Mogadishu by Somali government troops and their Ethiopian allies to quash an increasingly lethal insurgency.

The rebels are linked to the Council of Islamic Courts, which was driven from power in December in an Ethiopian-led offensive by UN-recognized Somalian government troops, accompanied by U.S. special forces.

The exact number of casualties was unclear due to the chaos in Mogadishu. Hospitals were overwhelmed and bodies were scattered in the streets.

The International Committee of the Red Cross said dozens of people have been killed since Thursday and more than 220 wounded, most of them civilians with bullet, grenade and other shrapnel wounds.

"The population of Mogadishu is caught up in the worst fighting in more than 15 years,'' the agency said.

Mohamed Deq Abukar Aroni, who was carrying two mattresses on his head as he fled, said he had never before abandoned his home in one of the world's most violent cities.

"But today I'm fleeing because shells are hitting residential areas indiscriminately,'' said Aroni, whose children carried two small paper bags of belongings. "I saw two of my neighbours get killed. I'm not going to stay here anymore.''

An Associated Press reporter saw an anti-aircraft missile hit an Ethiopian helicopter that had been bombing insurgent positions.

"The helicopter looked like a ball of smoke and fire before crashing,'' said Mogadishu resident Ruqiya Shafi Muhyadin, who watched as the helicopter rolled over in the sky and went down near the airport.

Dr. Mohamed Dhere, who spoke to The AP by telephone from an underground room, said three mortar shells hit Alhayat Hospital, wounding a doctor and a staff member.

"Since early this morning I have been hiding here from the mortar shells so I can't help rescue people,'' Dhere said. "I urge the two sides to respect health facilities.''

Mogadishu resident Abdi Hussein Aboke said he saw 10 bodies in the street Friday, all apparently civilians.

"Some were lying in alleys between houses while others were lying on the streets,'' he said.

"Residents are fleeing in all directions to escape the shelling,'' added Khalif Mohamed Mumin, who was also abandoning his home in search of safety.

Since being driven out, insurgents linked to the Islamic group have staged almost daily attacks on Somalian government and Ethiopian troops.

Last week, a cargo plane carrying equipment for African Union peacekeepers was shot down by a missile during takeoff, killing the 11-member crew.

The United Nations refugee agency said 57,000 people have fled violence in the Somali capital since the beginning of February, including more than 10,000 people who fled the city in the last week.

The figures were based on information provided by non-governmental organizations in Somalia, the UN High Commissioner for Refugees said.

The United States has accused the Islamic group of having ties to al-Qaida. On Thursday, a White House report said that despite recent setbacks to Islamic radicals in Somalia, foreign terrorists are still able to find a haven there because of the country's lack of governance, which contributes to a growing security threat throughout East Africa.

The report, said several al-Qaida operatives have used Somalia as a base of operations, including the perpetrators of the 1998 bombings of two U.S. embassies in East Africa and the 2002 attacks against an Israeli airliner and a hotel in Kenya.

"The individuals pose an immediate threat to both Somali and international interests in the Horn of Africa,'' the report said.