SANAA, Yemen (AP) ― Yemeni security forces killed six people Saturday and wounded hundreds in the second day of a harsh crackdown on anti-government protests, witnesses said. One of the dead was a 15-year-old student.

The assault with gunfire and tear gas was the toughest yet by the Yemeni government in a month of protests aimed at unseating President Ali Abdullah Saleh, who has been in power for 32 years.

The violence began with a pre-dawn raid on a central square in the capital, Sanaa, where thousands of pro-democracy protesters have been camped out.

Doctors and eyewitnesses said security troops surrounded the square with police cars and armored personnel carriers shortly after midnight and began calling on protesters through loudspeakers to go home. At 5 a.m., security forces stormed in, firing live and ammunition tear gas.

One protester died from a bullet to the head, which may have come from a sniper on the rooftop of a nearby building, witnesses said.

Abdelwahed al-Juneid, a volunteer doctor working with the protesters, said around 250 people were wounded.

“We were performing dawn prayers when we were surprised by a sudden hail of bullets and tear gas,” said Walid Hassan, a 25-year-old activist. “The protesters began throwing rocks at security ... it was total mayhem, a real battlefield.”

A few hours later, another protester was shot dead in a nearby street. Eyewitnesses said he was also killed by a sniper, but that could not be independently confirmed. Security officials did not have any immediate comment.

In the city of Dar Saad in the southern province of Aden, police used live fire and tear gas to disperse a crowd of several thousand, killing three demonstrators, a local activist and a hospital official said. They spoke on condition of anonymity because of the tense situation.

The hospital official said all the dead were all shot in the head. Eleven other protesters were wounded, he said.

The activist said the protesters later marched to the local police station, demanding that the shooter be handed over. Then they burned down the police station, the witness said.

In the port city of Mukalla in the southeastern province of Hadramout, a 15-year-old student was shot dead when security troops opened fire on protesters. Twelve people were wounded in similar violence in Yemen’s southern province of Taiz.

Saleh, an ally in the Obama administration’s fight against al-Qaida, appeared to be one of the Arab leaders most threatened by the regional unrest inspired by pro-democracy revolts in Egypt and Tunisia. Demonstrators are demanding jobs and greater political freedoms. Saleh has tried to calm protesters by proposing that the government create a new constitution guaranteeing the independence of parliament and the judiciary ― but protesters have said it’s too little, too late.

Saturday’s raid on the Sanaa square came after Yemen’s largest demonstrations in a month Friday were met by police gunfire that injured at least six protesters.

Hundreds of thousands of protesters gathered in Yemen’s four largest provinces, ripping down and burning Saleh’s portraits in Sheikh Othman, the most populated district in the southern port city of Aden, witnesses said. In the capital, thousands of women participated in demonstrations ― a startling move in a deeply tribal society where women are expected to stay out of sight.

By Friday evening, protesters in Sanaa had expanded the area of their sit-in encampment, further angering authorities and leading to clashes with plainclothes security men. Protesters said the men were carrying sticks, knives and iron rods. Four protesters were injured, witnesses said.

Yemen was chaotic even before the demonstrations began, with a resurgent al-Qaida, a separatist movement in the south and a sporadic Shiite rebellion in the north vexing the government, which has little control outside major urban areas.