(CNN) -- A cease fire announced Tuesday in Yemen's capital city of Sanaa did not appear to be holding, but a U.S. State Department spokeswoman said it nevertheless constituted a "good step" towards ending violence in the country.
It appeared that clashes were continuing Tuesday despite the cease fire announcement, which was to have taken effect at 3 p.m. between government forces and opposition groups, according to State Department spokeswoman Victoria Nuland.
Cease fires have been announced before in Yemen, often to little effect.
The cease fire announcement came after Yemeni President Ali Abdullah Saleh summoned the U.S. ambassador and reiterated a promise to sign an agreement brokered by the Gulf Cooperation Council in which he would step aside in exchange for immunity from prosecution, Nuland said.
"As you've seen, it's not clear that that has been completely enforced on either side since then but we do consider it a good step both that President Saleh is reaffirming his commitment to the G.C.C. agreement and that he understands and is supportive of the fact that the violence has got to end so that we can set the conditions for discussions about Yemen's diplomatic future," she said.
Earlier Tuesday, at least 10 people died and dozens were injured in clashes between Yemeni government security forces in the country's capital and the province of Taiz, medical officials reported.
Two died when security forces opened fire on thousands of anti-government protesters in Sanaa, the medical officials said.
Dr. Mohammed Al-Qubati, a medic at a field hospital there, said "security forces were shooting at protesters immediately after the protests started in Sanaa." Eleven of the injured were in critical condition, he added.
Eyewitnesses in Sanaa said the violence against protesters happened on Qa'a Road, directly behind the Republican Hospital.
The protesters had come together to continue voicing their demand that Yemen's embattled president, Ali Abdullah Saleh, step down.
Meanwhile, medics in Taiz reported at least eight people killed by government forces there.
Yasser Nusari, a medic in Taiz's Freedom Square, said five of the dead were youth protesters.
"Three were shot by the government. Streets are now chaotic and forces are everywhere attacking anyone who is against the regime," said Nusari. "At least 38 people were shot by government forces. It's unbelievable how the government is killing its own people."
Eyewitnesses said security forces bombarded the center of Taiz, as well as the districts of Moshiqi and Al-Rowdah. The witnesses said the government used rocket-propelled grenades and heavy artillery against protesters and pro-revolution fighters.
Clashes erupted between government forces and fighters loyal to the revolution and were still going late Tuesday afternoon.
In Sanaa, Al-Qubati described a horrific scene at his field hospital in Change Square, the epicenter of the anti-government movement.
"The death toll will rise due to the lack of medical equipment we have to help save the injured," the doctor said. "The government is committing a massacre here against unarmed youth."
Abdu Ganadi, the country's deputy minister of information, told CNN that opposition-supported militants are responsible for the violence.
"The opposition are supporting militants who are attacking government property in both Taiz and Sanaa," Ganadi said. "The opposition is seeking to take over the province of Taiz, and the government was only trying to defend the interests of the people."
As for the capital, Ganadi said there are no more protesters.
"These are militants and are all armed. The youth are just a cover-up for the violence the opposition is creating," he added.
This latest round of violence comes just one day after Saleh made comments welcoming a United Nations Security Council resolution, which calls on him to implement a Gulf Cooperation Council-backed initiative that would see him transfer power.
According to SABA, Yemen's official state news agency, Saleh confirmed Monday the readiness of Yemen's Ruling Party to immediately meet with the country's opposition in order "to complete the dialogue over the operational mechanism for the (Gulf) initiative as soon as possible and to reach the final signing of the initiative and its immediate implementation, which would lead to early presidential elections on a date agreed upon by all."
While Saleh has repeatedly promised to sign the GCC-backed deal, he has not done so.
Friday, the U.N. Security Council unanimously condemned the months of violence in Yemen. But the resolution stopped short of explicitly calling for Saleh's resignation.
The proposed Gulf council-brokered accord, which is backed by the United States and the European Union, would allow Saleh to resign from power in exchange for immunity from prosecution.
The Security Council resolution, passed by a 15-0 vote, demands that Yemen allow peaceful demonstrations and end crackdowns on civilians.
CNN's Mohammed Jamjoom is reporting from Abu Dhabi, with Hakim Almasmari in Sanaa