Yemeni security forces firing live bullets wounded four anti-regime protesters in separate incidents in the main southern city of Aden on Saturday, medics and witnesses said.
One protester was shot when security forces opened fire to disperse a sit-in in Mualla neighborhood, witnesses said, as opposition activists continue to demand the resignation of embattled President Ali Abdullah Saleh.
Three other people there suffered from tear-gas inhalation.
Soon afterwards, protesters attacked police headquarters, prompting security forces to fire live rounds at them, wounding three, medics and witnesses said.
The demonstrators, chanting "The people want to overthrow the regime," hurled stones at the forces.
The clashes come a day after violence in the capital Sanaa left at least 52 people dead and scores hurt, according to medics.
Calls to suspend US aid
The United States should "immediately" suspend military aid to Yemen until Saleh stops attacking anti-government protesters and prosecutes those responsible, Human Rights Watch said Friday.
Saleh ordered a state of emergency in Yemen after regime loyalists killed at least 46 protesters in the bloodiest clash in weeks of unrest.
"Time and again, President Saleh promises he will stop attacks on peaceful protesters and yet the number of dead keeps rising," said Sarah Leah Whitson, the HRW Middle East director.
"The United States should back up its words condemning the carnage with action, and halt military aid to Yemen."
Washington has provided "more than $300 million in military and security aid to Yemen in the past five years," the New York-based group said.
"The U.S. should make further military aid contingent on the government ending attacks on protesters and holding accountable officials and others, regardless of position, who are responsible for the unlawful use of force," HRW said.
"I strongly condemn the violence that has taken place in Yemen today and call on President Saleh to adhere to his public pledge to allow demonstrations to take place peacefully," President Barack Obama said earlier in a written statement.
"Those responsible for today's violence must be held accountable," he said.
The U.S. president also called for a "peaceful, orderly and democratic path to a stronger and more prosperous nation" in Yemen, where the government is allied with Washington in battling Al-Qaeda in the Arabian Peninsula (AQAP).
Saleh, struggling to maintain his 32-year grip on power in the impoverished Arabian Peninsula state, said the deaths had occurred in clashes between demonstrators and other citizens at a protest encampment at Sanaa University.
"I express my extreme sorrow for what happened today after Friday prayers in the university district," Saleh told a news conference in Sanaa, blaming gunmen among the protesters for the violence.
"The police were not present and did not open fire," he said. "It is clear there are armed elements inside these tents and they are the ones who opened fire."
He declared a 30-day state of emergency that gives wider powers to security forces and bars citizens from bearing arms in public. A curfew was being discussed.
In breach of international law
In Geneva U.N. human rights experts condemned the deadly crackdown on protestors and said that Yemen's actions breached international law.
"Not only are attacks on peaceful demonstrators clearly prohibited, but also abiding by instructions to use excessive force constitutes a clear violation of international law," said Christof Heyns, the U.N. special rapporteur on extrajudicial executions.
Heyns warned that security officers who fail to protect peaceful demonstrators against violence can be "held criminally accountable".
Frank La Rue, the special rapporteur on freedom of opinion and expression, also had strong words against the action taken by Yemeni authorities.
"The government of Yemen has killed, seriously injured, or arbitrarily detained peaceful protesters. Such flagrant human rights violations are utterly deplorable," he said in the statement which was also jointly issued with the special rapporteur on torture Juan Mendez.