World anger over bloodshed in Yemen and pressure on President Ali Abdullah Saleh to stand down mounted on Wednesday after at least 24 people were killed in as many hours.
Strong statements from the United States, United Nations, European Union, Britain and Italy came as Saleh's foes cautiously welcomed a proposal by Gulf states to mediate in their demands for the veteran president to step down.
Five people were killed on Tuesday in a firefight in Sanaa between troops of an army division that has sided with anti-regime protesters and tribesmen close to Saleh, security officials said.
The deaths came as dissident General Ali Mohsen al-Ahmar accused forces loyal to Saleh of trying to kill him in an ambush in which an unspecified number of other people lost their lives.
Members of the presidential guard, who had masqueraded as part of a delegation of tribal envoys visiting the headquarters of Ahmar's rebel division, pulled out weapons and opened fire on the general, his office said.
Tuesday's clashes near the Sanaa University base of youth protesters came a day after 19 demonstrators were gunned down in clashes with security forces in the southern city of Taez and in Hudaydah on the Red Sea.
Security forces in Taez, among them rooftop snipers, shot dead 17 people after protesters demanding Saleh's ouster marched on the provincial headquarters in the city.
That prompted the UN High Commissioner for Human Rights to condemn the "disproportionate and excessive" use of force in Taez.
"We are very alarmed by reports of disproportionate and excessive use of force, including machine guns, against peaceful protesters by government security forces," said Navi Pillay's spokesman.
In Washington, White House spokesman Jay Carney said in a statement: "The United States strongly condemns the use of violence by Yemeni government forces against demonstrators in Sanaa, Taiz, and Hodeida in the past several days".
"The Yemeni people have a right to demonstrate peacefully, and we remind President Ali Abdullah Saleh of his responsibility to ensure the safety and security of Yemenis who are exercising their universal right to engage in political expression."
"We call upon the Government of Yemen to conduct full investigations into these events and to hold those responsible accountable for their actions," Carney said.
In a further sign of ebbing support for Saleh, the statement called on him to resolve the political impasse with the opposition so that "meaningful" political change could take place in an orderly and peaceful manner.
In London, British Foreign Secretary William Hague said he was appalled by the bloodshed and condemned the "indiscriminate violence" of security forces.
"In early March, President Saleh promised to maintain maximum restraint in the use of the Yemeni security forces in controlling peaceful demonstrations. We strongly urge him to keep that promise," he said.
And Italy urged Sanaa to "cease all forms of violence" against demonstrators and to open the way for "a constructive dialogue as soon as possible with those who are peacefully calling for a new season of reforms".
On the political front, opposition spokesman Mohammed Qahtan said "we have welcomed (a Gulf Cooperation Council invitation) and said we will attend, but to discuss a transfer of power only".
An official source said the government was also in favour of talks, which would be held in the Saudi capital Riyadh at a date to be determined.
But other figures in the opposition remained cautious.
"We welcome any effort that would lead to (Saleh's) immediate departure, but we haven't received anything to discuss yet," said Mohammed al-Sabri, another top opposition official.
The European Union urged Saleh to begin a political transition "without delay", a day after Washington pressed him to negotiate a peaceful handover, warning that Al-Qaeda stood ready to benefit from a power vacuum.
According to medics and witnesses, about 125 people have now been killed in Yemen's crackdown on protesters, who launched nationwide demonstrations in late January to unseat Saleh, in power since 1978.
Washington, which has considered Saleh a key ally in its "war on terror" but expressed fears of Al-Qaeda taking advantage of a prolonged crisis, is now pressing him to negotiate a transition of power.
"We are obviously concerned that in this period of political unrest that Al-Qaeda and other groups will attempt to take advantage of that power vacuum," White House spokesman Jay Carney said on Monday.
But the Pentagon said there were no plans to suspend US military aid to Yemen.
"As far as I know, it has not been," press secretary Geoff Morrell said when asked at a news conference if the US administration was considering withholding military aid due to the unrest and violence.
"Obviously, we are monitoring the situation closely. It's fluid," Morrell said.
Amnesty International warned on Wednesday against any immunity deal for those responsible for the deaths of dozens of anti-regime demonstrators in Yemen, especially the "Black Friday" bloodbath.
"The international community must play a more active role if Yemenis are to get accountability for the bloody killings of recent weeks," the London-based human rights organisation said.
In the Bloody Friday bloodbath of March 18, 52 people were gunned down in what the rights group called "an apparently coordinated sniper attack on a protest camp in Sanaa".