(CNN) -- Yemeni security forces opened fire on anti-government protesters in Sanaa Sunday, killing at least 22 people and wounding 200 more, according to a reporter in the capital.

Freelance journalist Laura Kasinof told CNN that protesters told her they were attacked as soon as they exited a "protected" area, where they have been demonstrating for months.

Protesters are calling for the ouster of longtime Yemeni President Ali Abdullah Saleh, who is recuperating in Saudi Arabia from a June attack on his palace. He has vowed to return to Yemen to finish his term.

Demonstrators were attacked by security forces as well as by men in plain cloths, acting as snipers, Kasinof reported protesters told her.

Citing a doctor, she said 22 people had been killed and more than 200 were shot.

"There's clearly not enough staff to take care of this many injured people," Kasinof said.

Video posted on YouTube purported to show the protest. In it, what appears to be water and tear gas are shot to disperse the crowd. Gunshots can be heard, as well as someone shouting: "This revolution is peaceful, peaceful. We are here for our beloved martyrs. We will not back down!"

Protesters can be seen in the video throwing what appear to be bottles or rocks.

CNN could not independently confirm the authenticity of the video.

Yemen's state-run news agency reported that "militias of the Islah opposition party and 1st armoured division" staged an unauthorized protest Sunday. A security source from the interior ministry told the Saba news agency that the militias threw Molotov cocktails at a power station, causing generators to burn.

They also attacked anti-riot forces, wounding four soldiers, Saba reported, according to the ministry source said.

CNN made repeated attempts to contact people in Sanaa Sunday, but phone lines appeared to be down.