Kabul on Thursday mourned victims of a powerful truck bomb that killed at least 80 people and wounded hundreds amid growing public anger at the government's failure to prevent yet another deadly attack in the heart of the Afghan capital.

Wednesday's blast, at the start of the Muslim holy month of Ramadan, ripped through a traffic-clogged street, packed with people on their way to school or work during the morning rush hour, causing hundreds of casualties in an instant and sending a tower of black smoke into the sky.

In scale, it was one of the worst such attacks since the U.S.-led campaign to oust the Taliban in 2001 but in kind, it was only the latest in a grim series that has killed thousands of civilians over the years.

President Ashraf Ghani made a televised address late on Wednesday, calling for national unity in the face of the attack, which his National Directorate for Security blamed on the Taliban-affiliated Haqqani network, but he faces an increasingly angry public.

"For God's sake, what is happening to this country?," said Ghulam Sakhi, a shoemaker whose shop is close to the site of the blast. "People leave home to fetch a loaf of bread for their children and later that evening, their dead body is sent back to the family."

The explosion occurred near the German embassy at one of the entrances to Kabul's unofficial Green Zone, a haphazard warren of concrete blast walls and sandbagged check points that has grown up around the diplomatic quarter over the years as the insurgency has intensified.

While the sewage tanker carrying the bomb was stopped from entering the zone, it was unclear how such a large quantity of explosives could get through the ring of checkpoints set up around Kabul to protect the capital.

A huge crater ripped into the ground at the site of the blast and shattered windows in houses more than a kilometer away were testament to the power of the explosion, which was set off by a bomb concealed in the tanker.

Several embassies were damaged and a number of foreigners wounded, but the majority of victims were, as ever in such attacks, Afghan civilians.

"Right now, thousands of our people are in mourning. Why and for how long do we have to suffer this situation?" said shopkeeper Enayatullah Mohammadi. "We want our leaders to ensure security in the country and if they can't, they should resign."

Deputy Interior Minister Murad Ali said on Thursday that 80 people had been killed and 463 wounded in the attack.

The true number of victims may never be known, however. Several guards who apparently stopped the tanker from entering the Green Zone have simply disappeared, according to police.