The violence signaled an accelerated attempt by President Ali Abdullah Saleh and his loyalists to crush their rivals and tighten his grip on the country after his return a day earlier from Saudi Arabia, where he has been undergoing treatment for the past three months for wounds suffered in an assassination attempt.
One of Saleh's top rivals — Maj. Gen. Ali Mohsen al-Ahmar — called for international help, asking the U.S. and other regional powers to rein him in. He warned that Saleh is pushing the country into civil war and compared him to the Roman emperor Nero, burning down his own city.
In a strongly worded statement, al-Ahmar called Saleh a "sick, vengeful soul" who treats Yemen like his personal estate.
"With his return, Yemen is experiencing sweeping chaos and the harbingers of a crushing civil war which this ignorant man is determined to ignite," said al-Ahmar, who was once a close ally of Saleh but early on in the uprising joined the opposition along with the 1st Armored Division he commands.
Sanaa has become a city divided between rival gunmen, with barracks and roadblocks manned by men in different uniforms indicating their loyalties. The city's streets have become too dangerous for the residents to venture out. Many took cover in basements because of the ongoing thuds of mortars during fighting that has killed at least 140 people the past week.
The turmoil is a blow to US efforts to find a stable transfer of power to ensure the continued fight against al-Qaida militants in Yemen, who Washington says constitute the most dangerous branch of the terror network. With the country spiraling deeper into disorder, al-Qaida linked militants have already seized control of entire towns in southern Yemen beyond their traditional strongholds.
Saleh, who has clung to power despite nearly eight months of protests and the June 3 assassination attempt, abruptly returned to Yemen on Friday. Street battles that reignited a week earlier in Sanaa rapidly escalated, widening to include the most determined attack by Saleh's forces on al-Ahmar's military units, anti-government tribesmen and the unarmed protesters themselves.
Regime forces on Saturday pounded the protest camp in Sanaa's Change Square where thousands were massed, as they have been nearly daily since February in peaceful protests demanding the end of Saleh's 33-year rule. Mortar shells blasted in the square, setting a number of tents on fire. Snipers on nearby rooftops fired down methodically on protesters dashing for cover.
"I was terrified when I saw one protester who left the tent running toward us as he heard the mortars, only to be shot in the chest by a sniper and fall to the ground before my eyes," said Samir al-Mukhlafi, a protest leader.
Republican Guard troops and Central Security forces, led by Saleh's son Ahmed, fired anti-aircraft guns and rocket-propelled grenades down streets near the square in battles with soldiers loyal to al-Ahmar protecting the protesters. The shelling wrecked several houses, witnesses said.
At one field hospital in the square, the body of a protester cut in two by mortar blasts was brought in. At least 28 protesters and one of the soldiers guarding them were killed Saturday, and 54 people were wounded, said Mohammed al-Qabati, a medic at the field hospital.
The intensity of the fighting forced ambulance crews to leave many of the bodies in the streets, he said, and motorcycles were bringing in the wounded.
"There are three bodies lying on the ground that we can't pick up because of snipers on the roof," said al-Qabati.
A prominent Yemeni human rights center said the violence left the impoverished country of over 24 million on the verge of collapse, urging the international community to stop the bloodshed.
"The situation in Yemen is becoming catastrophic," a statement by the Yemen Observatory for Human Rights, describing fighting between army units, security forces and tribesmen, the targeting of protesters and random killings of civilians in their homes or on the streets.
In the northwest of the capital, Sanaa, mortar shells rained down on the headquarters of the Al-Ahmar's 1st Armored Division. Eleven of al-Ahmar's troops were killed and 112 were wounded, according to Abdel-Ghani al-Shimiri, a spokesman for the soldiers.
An official in al-Ahmar's office said his troops will remain only on the defensive and won't go after Saleh's troops. The official said al-Ahmar conveyed the message to diplomats in Sanaa, who are apparently trying to contain the violence.
If al-Ahmar were to try to go on the offensive and move directly against Saleh and his leadership, that would likely escalate the violence even more. In his statement, al-Ahmar called on the neighboring Gulf countries, the United States, and the international community to deter Saleh, "stop his irresponsible behavior that aims to ignite a civil war that would have repercussions on the whole region."
On a third front, Saleh's troops fought anti-government tribesmen in the capital's Hassaba district, where 18 tribal fighters have been killed the past two days, according to a statement Saturday from tribal elders.
Hassaba is a stronghold of Yemen's most powerful tribal confederation, the Hashid, led by Sheik Sadeq al-Ahmar, another Saleh foe. He is not related to Maj. Gen. al-Ahmar.
Eight government troops were also killed and dozens wounded, said Interior Minister Gen. Mutahar al-Masri. He did not specify when or where the casualties occurred.
Violence also shook the southern city of Taiz, home to one of the strongest waves of anti-Saleh protests, and at least one protester was killed there, a medical official said.
In response to the violence, the Gulf Cooperation Council — the alliance of Saudi Arabia and five other energy-rich nations — called for a cease-fire and urged Saleh to immediately sign a power transfer deal proposed by the group.
"The security and humanitarian situation in Yemen can't take any more delays," a statement issued by the group, currently in New York, said.
The GCC's accord, which is backed by the U.S., would require Saleh to resign and transfer his powers to the vice president in return for immunity from any prosecution. Saleh endorsed the deal several times only to balk at signing at the last minute.
Abdullah Obal, an opposition leader, said international pressure appears to be the best way to push Saleh to step down and stop the fighting. But he said a major obstacle to any resolution and end to the violence was the control of Saleh's family — particularly his son Ahmed and several nephews — over much of the armed forces.
"We can't move a single step ahead without dissolving the armed forces, which will remain a sword threatening any resolution, because they only take orders from him," said Obal.
Yemen's uprising began in February as the unrest spreading throughout the Arab world set off largely peaceful protests in this deeply unstable corner of the Arabian Peninsula. Saleh's government responded with a heavy crackdown that has killed hundreds.
On Saturday, Saleh met with senior security leaders and ordered an end to all display of arms around the capital. Despite the order, there was no sign of any change on the ground.
Opposition spokesman Mohammed al-Sabri held Saleh directly responsible for the killings.
"It's as if he was unleashed from a cage and came out to retaliate," al-Sabri said. "This man deals with Yemen as if he's a gang leader, not a leader of a nation."