ISLAMABAD, Pakistan — The Pakistani government tried to blast through the walls around a mosque in Islamabad yesterday amid violent clashes with extremists who officials said were holding women and children inside as human shields.

Despite calls from its captured leader, Abdul Aziz, to surrender, scores of hard-line students holed up inside the mosque clashed with troops for a third consecutive day in the heart of the capital. At least 19 people have died in the violence.

The fighting erupted after a sixmonth stand-off between the government and two brothers who run the mosque in Islamabad.

President Musharraf had grown embarrassed by the two brothers’ increasingly defiant anti-government antics and their demand for the imposition of Islamic law.

The interior minister, Aftab Sherpao, said the radical students besieged in the Lal Masjid, or Red Mosque, were armed with Kalashnikov assault rifles, hand grenades, and Molotov cocktails.

“There are 50 to 60 hardcore militants inside the mosque,” he said. “They are keeping women and children who want to come out and are not allowing them to leave.”

Several students who had fled the mosque claimed some men, women, and children had been prevented from leaving the mosque and madrassa — an Islamic religious school — which houses Pakistan’s largest girls’ seminary. Niaz Muhammad Khan, 28, from Mardan, said, “I was with my brother in Lal Masjid when this operation was launched. I tried to take my brother out of the madrassa, but the management refused to allow us to go out. Last night, I managed to escape.”

Earlier, troops blew up most of the wall surrounding the mosque and smashed in one of its doors with an armored personnel carrier, according to eyewitness reports. Some of the heaviest clashes erupted when students opened fire on troops and hurled hand grenades, said the chief military spokesman, Major General Waheed Arshad.

The detained mosque leader and his brother, the deputy leader, Abdul Rashid Ghazi, who remains inside, both denied that anyone was being kept against their will.

Mr. Aziz was captured on Wednesday as he tried to flee the mosque complex, wearing a burqa. He told state television that about 1,000 male and female students remained inside. “After coming out, I saw the siege was massive and came to the conclusion that we should give up,” he said. “People will not be able to stay inside for long.”

Somewhat inexplicably, Mr. Aziz made his TV appearance wearing a black burqa. The interviewer asked him to take off the veil, which he did to expose a smile.

The cleric later appeared in court charged with plotting terrorist attacks and kidnapping people, including seven Chinese nationals abducted by his students from an acupuncture clinic for allegedly running a brothel. He was remanded in custody.