(Reuters) -- A rally against the government on Friday following this week's devastating truck bomb attack in Kabul saw hours of angry confrontation between protesters and police, who fired into the air to drive back crowds trying to cross security cordons and reach the presidential palace.

At least four people were killed and 15 wounded in the gunfire, drawing condemnation from human rights group Amnesty International and leading the United Nations envoy in Afghanistan to appeal for calm.

A small group of protesters remained near the blast site in the centre of town, sheltering from the sun in open tents.

But otherwise security authorities in Kabul banned protests and demonstrations, citing the risk of attacks on large gatherings of people.

Although Saturday is a normal working day in Afghanistan, large parts of the city were blocked off, with armed checkpoints set up and armoured vehicles patrolling the streets.

The unrest has heaped pressure on the government of President Ashraf Ghani which has faced increasing public anger over its inability to ensure security in the capital following a string of high profile suicide attacks.

Wednesday's truck bomb, which killed more than 80 people and wounded some 460, was one of the worst since the U.S.-led campaign to oust the Taliban in 2001 but in other respects it scarcely differed from a long series of previous attacks.

In the first three months of the year at least 715 civilians were killed, after almost 3,500 in 2016, the deadliest year on record for Afghan civilians.