ADEN // Yemen's air force has bombed the positions of al Qa'eda and Islamist militants who have taken control of the southern coastal city of Zinjibar, residents said on Monday.
They also said the army is shelling the city with artillery.
Several hundred al Qa'eda and Islamist militants took over the Gulf of Aden city a few days ago and have been battling locals and government soldiers who are trying to regain control.
In Saan'a, hundreds of soldiers loyal to Yemen's embattled president stormed a protest camp in a southern city on Monday, firing on crowds and bulldozing a field hospital set up in anticipation of such an attack. At least 20 people were killed, according to a medical official and other witnesses.
The city of Taiz has been a hotbed of anti-government protests since crowds began calling for President Ali Abdullah Saleh's ouster in early February. The heavy crackdown there signaled Saleh remains intent on preserving his 33-year rule despite spiraling upheaval, intense international pressure to step aside and defections by key allies and some army units.
Security forces first tried to clear the square in Taiz with water cannons, tear gas and loud stun grenades, sending thousands rushing for shelter.
Forces from the Republican Guard, which is commanded by one of Saleh's sons, then moved in before dawn with tanks and bulldozers, said Sadek al-Shugaa, head of the field hospital at the protest camp.
Republican Guard soldiers along with security forces and armed men in civilian clothes attacked the protesters. Some set fire to dozens of tents used by protesters occupying the square for weeks, and bulldozers ran over hundreds of other tents without checking whether anyone was still inside, two witnesses said.
One of the witnesses, Mohammed al-Zarafi, said he saw tents being set on fire while injured protesters were still inside.
The other witness, protester Boushra al-Maqtali, called the attack "a real massacre."
"The square and the (field) hospital are in ruins," she said. "The tanks took the place of hundreds of tents that were set up there. The artillery units are occupying the whole space to make it impossible for the youth to return to the square," she said.
Troops also attacked the Majeedi Hotel overlooking the square, where journalists were detained, al-Shugaa said. Then snipers took over the top of the building to shoot at protesters, he said. Amateur video aired by Al-Jazeera TV showed masked men with rifles shooting from rooftops at protesters in the streets.
Al-Shagaa said most of those injured were in critical condition with gunshot wounds to the head, chest and neck. Several dozen of the injured were dragged away by security forces, he said.
Yemen's unrest has veered dramatically in the past week.
The failure of a mediation effort by Saudi Arabia and other Gulf nations seeking to persuade Saleh to transfer power gave way to five days of fierce street battles in the capital last week between pro-Saleh military units and armed men loyal to the country's most powerful tribal leader, who has joined the opposition. The fighting killed 124 people.
In the south, meanwhile, hundreds of Islamic militants seized the small town of Zinjibar near the Gulf of Aden coast on Friday.
On Monday, they shot dead four military officers who stopped at fake checkpoints the militants set up along the road from the town to the port city of Aden, according to a medical official at al-Razi hospital. He spoke on condition of anonymity because he was not authorized to talk to journalists.
Saleh's opponents, including some in the military, have accused him of allowing the militants to take control of the area as a way to spread fear that his ouster would deliver the country to al-Qaida. He has repeatedly argued this point, but has failed to win international backing for his continued rule.
The United States, which once saw him as an essential ally in battling the al-Qaida branch in the country, has turned its back on Saleh, pressing him to step down.
Military units battled the militants in Zinjibar overnight and into Monday morning in an attempt to clear them from the town, where they've blockaded themselves behind barricades and rocks.
Shelling killed at least four of the fighters, bringing the death toll there since Saturday to 34, according to the official at al-Razi hospital. That figure includes militants, soldiers and civilians, he said.