Sanaa, Yemen (CNN) -- Yemeni Vice President Abdu Rabu Hadi has called for a cease-fire from all sides after a third day of bloody unrest, the state-run Saba News Agency reported Tuesday.
Random clashes between government troops and fighters could still be heard in Sanaa in the hour after his appeal for peace was made.
Two protesters were killed and 11 wounded when government rockets landed in Change Square in Yemen's capital earlier Tuesday, medics said, with two of the injured in critical condition.
Eyewitnesses said at least 13 blasts were heard at Change Square in Sanaa and one blast occurred near a medical camp.
Abdul Rahman Barman, the executive director of a local human rights organization, said Yemeni President Ali Abdullah Saleh's regime is attacking with no limits and does not differentiate between civilians, protesters or gunmen.
"All are targets for the oppressive Saleh regime," Barman said.
Government spokesman Abdu Ganadi said that "government troops are attacking armed militants who claim to be unarmed."
Prominent opposition leader Hamid al-Ahmar's home in Sanaa was also attacked by rockets and rocket propelled grenades late Tuesday, his office manager, Fowzy al-Garadi, told CNN.
More than 11 strikes hit the residence, al-Garadi said, leaving 13 people dead and seven injured.
"The government attacks targeted Hamid al-Ahmar, and residents in the area were also affected by the random government attacks," he said.
U.S. State Department spokeswoman Victoria Nuland condemned the violence and called on all those involved in it to exercise restraint.
"The United States continues to support the Yemeni people's aspirations for a peaceful and orderly transition that is responsive to their aspirations for peace, reconciliation, prosperity, and security. A political solution is the best way to avoid further bloodshed," she said in a statement.
Tuesday's deaths came after a violent crackdown by Yemeni authorities on Sunday and Monday left dozens dead at protests, according to witnesses and medical officials.
Protesters are calling for the ouster of the longtime Yemeni president, who is recuperating in Saudi Arabia from a June attack on his palace. He has vowed to return to Yemen to finish his term.
Abdul Ghani al-Shamiri, a media representative for Gen. Ali Mohsen, who defected from the government six months ago, said Tuesday: "The defected military is not fighting the government. We are defending and not attacking.
"We cannot watch government troops attack innocent protesters and not help them. We will insist that the revolution remains peaceful but in the same time ensure that unarmed protesters are safe."
Al-Shamiri told CNN that since defected military members were fighting only to defend the protesters, the violence would stop once government troops stopped attacking.
Mohsen defected from the Yemeni military March 18 and since then has joined the call for Saleh to leave power.
Adel al-Rabyee, a youth leader in Sanaa, said earlier the attacks on protesters are continuing.
"Unfortunately, the political crisis is affecting the youth revolution and the clashes have left us in awe at where our peaceful revolution is heading," he said.
Thirty-one people were killed Monday in clashes in Yemen: 28 in Sanaa and three in Taiz, according to medical officials.
On Sunday, at least 26 protesters were killed and more than 550 were wounded -- hundreds of them by gunshots -- when security forces fired live bullets and tear gas at a massive demonstration in the city, a medic said.
The violence has triggered a new wave of international pressure on Yemen.
An official with the human rights group Amnesty International said the country was on a "knife edge" and the situation could spiral into a civil war.
Officials from the United Nations and the Gulf Cooperation Council were in Sanaa Monday, hoping to help organize a peaceful transfer of power.
The Yemeni government has repeatedly denied accusations of excessive use of force, and said the government is committed to establishing a peaceful transfer of power. Yemeni officials have said forces cracked down on those committing acts of violence during protests.