A demonstration in downtown Kabul turned violent on Friday as police fired at rock-throwing protesters demanding better security in the Afghan capital in the wake of a powerful truck bomb attack that killed 90 people. Several demonstrators were killed and police injured, authorities said.

More than 1,000 people demonstrated as Afghans mourned the victims of a massive truck bomb that also wounded more than 450 on Wednesday. It was one of the worst extremist attacks since the drawdown of foreign forces in 2014 and raised fears about the government's ability to protect its citizens nearly 16 years into a war with insurgents.

Police fired their weapons into the air as a warning at first as about a hundred of the demonstrators rushed toward them, some throwing rocks. As the protesters attempted to move closer to the Presidential Palace, police sprayed them with hoses from a water tanker and later fired tear gas.

Reports of casualties varied, with Abdul Hafiz Mansur, a member of Parliament from Kabul, saying eight protesters were shot dead by police.

However, Gen. Hassan Shah Froogh, Kabul police chief, said two protesters were killed and 25 police were wounded by rocks thrown from demonstrators.

Protesters held pictures of destruction from the truck bomb blast and of government leaders. Shopkeeper Mohammad Anwar said four members of his family were killed in the bombing and he wanted a change of leadership.

"We are calling on President Mohammad Ashraf Ghani to resign," he said. Demonstrators also called for Chief Executive Abdullah Abdullah to step down.

Protester Amir Arya said a number of his friends were wounded by police as they tried to block the protesters from advancing.

"Some of them were beaten by police with sticks and some others detained," he said. "This act of police and government proves that peaceful demonstration would not be useful anymore."

Most of the casualties from the truck bombing were civilians, including women and children, officials have said. But the dead also included Afghan security guards at the facilities, including the U.S. Embassy, and 11 American contractors were wounded, none with life-threatening injuries, a U.S. State Department official said.

No one has claimed responsibility for the attack, which came in the first week of the Muslim holy month of Ramadan.