(CNN) -- The death toll from clashes between Yemeni security forces and protesters rose to 13, an activist said.
The clashes occurred in the cities of Sanaa and Taiz on Wednesday, said Ibrahim Mothana, an activist who said he spoke to doctors. The death toll could rise as he was trying to get reports on victims in at least three other hospitals, Mothana said.
CNN could not independently verify his report.
Witnesses said Yemeni security forces used live ammunition fired on protesters in Sanaa and Taiz on Wednesday.
Doctors and witnesses in the cities told CNN that 169 more people had been injured, some critically.
"Security forces are aiming for a massacre in Sanaa," said Abdul Wahab Anesi, a medical staff spokesman at a field hospital set up in Change Square.
Before Republican Guards began firing at protesters in the square, they reportedly clashed with military personnel who had been protecting demonstrators gathered there. Journalists, medical sources and other witnesses told CNN that these soldiers defected two months ago along with Maj. Gen. Ali Mohsen Al-Ahmar, who withdrew his support from President Ali Abdullah Saleh in late March. At the time, he promised to protect civilians demonstrating against the president.
In addition to the casualties in the capital, three people were killed and four were reported critically injured in Taiz.
"The attack took place while we were chanting, 'One more week left for you, Saleh,'" said Sabir Ali, a protester in Taiz. The protesters were giving Saleh a week to step down, saying if he does not, they will make good on a vow to march to the presidential palace.
Earlier, a senior security official denied that forces fired on protesters in Taiz.