(CNN) -- Constant gunfire and loud explosions reverberated early Monday in the capital of Yemen, residents and eyewitnesses said.
According to eyewitnesses, government security forces and tribesmen loyal to Hashid tribal leader Sadeq Al-Ahmar clashed in the Hasabah neighborhood in northern Sanaa. According to Abdulqawi Al-Qaisi, spokesman for the Al-Ahmar family, government forces have been attacking the tribal leader's family residences.
Residents and witnesses also reported that the Republican Guard was bombarding the headquarters of the 1st Armored Division, loyal to Maj. Gen. Ali Mohsen Al-Ahmar, who withdrew his support from President Ali Abdullah Saleh in late March.
The embattled Saleh said Sunday that "strong documentation of the cooperation" between al Qaeda and the Muslim Brotherhood indicate a military coup that is destabilizing the country. He described the opposition as "insane people, who can't sleep and only want to take power."
Bloodshed continued Sunday evening, including the deaths of three people in Sanaa when a rocket-propelled grenade hit bystanders, medics said.
Earlier in the day, Yemeni security forces opened fired on demonstrators gathering for a planned march in the capital, killing five people and injuring 54 others, according to a medic on the scene.
In a separate demonstration in the city of Taiz, a woman was killed by a shot to the head from a government sniper, medics and eyewitnesses in Freedom Square Taiz said.
Medics named her as Aziza Othman Kaleb. Four others who were next to her were also injured by the snipers in the march, the same sources said.
Opposition activists in her hometown and in the capital said she was 20 and claimed she was the first woman to be killed while marching against the government. CNN could not independently confirm that claim.
Activist Atiaf Alwazir called the shooting of a woman "a sign that the government security forces will not really stop shooting, even if there are women."
"Women may have been beaten, arrested at times -- but never directly shot at and this is a scary escalation," she told CNN.
The crackdown in Sanaa was also bloody, doctors said.
"The injured are entering the hospital by the minute. We need help. We call on people to donate blood for the injured," Mohammed Al-Qubati, who works at a field hospital in Change Square.
Five of the wounded are in critical condition, he said from the square that has become the center of protests against Saleh.
Protesters carried signs with slogans including: "Saleh kills and the world watches. Is this the justice the west preaches?" according to witnesses and activists.
Others carried flowers or signs that said: "We are not armed, Don't attack us with gunfire," witnesses told CNN Sunday.
Some chanted: "Oh Saleh the oppressor your time will come, our blood is not cheap."
CNN has not independently confirmed the details of casualties in Sanaa or Taiz, and the government has not yet responded to CNN requests for comment.
The reported violence comes a day after at least 10 people were killed and 38 others wounded in clashes in the capital, Al-Qubati and others said.
Molhim Saeed, another medic in Change Square, called Saturday "a sad day for the revolution."
"The marches were peaceful and the youth were unarmed. They refused to even fight back when they were being shot at," Saeed said.
Saleh, meeting Sunday with Yemeni leaders, said members of the U.N. Security Council don't understand the true picture in the country, the country's state news agency Saba reported.
He also said those who participate in "heavily armed marches" are killing soldiers. "Are these peaceful acts?" he asked, according to the news agency.
A State Department spokesman late Saturday urged Saleh to hand over power.
"We are deeply concerned by recent violence in Yemen. We extend our deepest sympathies to those who lost loved ones as result of this violence," said Aaron Snipe, of the State Department's Bureau of Near Eastern Affairs.
"All those wishing to express themselves must be allowed to do so peacefully. We urge a prompt, impartial investigation into the events that led to the recent violence," he said. "We again urge President Saleh to initiate a full transfer of power without delay, allowing the Yemeni people to move down a path toward a unified, stable, secure, and democratic Yemen."
Last week, tens of thousands of protesters gathered in Sanaa, marching, chanting and calling for the United Nations to come out with a firm resolution in support for change in the country.
For its part, the government says it is trying to come up with a solution to end the political stalemate.
"The ruling party is serious on finding a solution to the political crisis from its roots to ensure they don't erupt in the future," said Tareq Shami, spokesman for the ruling party, the General People's Congress.
Saleh is also facing armed revolt from members of powerful tribes in his country.
CNN Senior State Department producer Elise Labott contributed to this report.