Kabul Attack Death Toll More than Doubles to 64

The death toll from a Taliban suicide attack in Kabul has more than doubled to 64, officials said Wednesday, the deadliest militant assault in the Afghan capital for years.

The brazen assault on Tuesday in a densely packed Kabul neighborhood marked the first major Taliban attack in Kabul since the insurgents announced the start of this year's fighting season last week.

A powerful Taliban truck bomb tore through central Kabul and a fierce firefight broke out, sending clouds of smoke billowing into the sky and rattling windows several kilometres away.

"It is with regret that I announce that 64 people were killed and 347 others wounded in yesterday's Kabul attack. Most of them are civilians," ministry spokesman Sediq Sediqqi told reporters.

The ministry had earlier put the death toll at 30.

"The victims of (the) terrorist attack are all fathers, brothers or children of people," Afghan President Ashraf Ghani said on Twitter.

"We will avenge every drop of Afghan blood."

Mourners in Kabul held emotionally charged funerals for the victims of the attack on Wednesday, one of the deadliest in Kabul for years.

In December 2011, more than 50 people were killed in a suicide attack during the Shiite holy day of Ashura.

The Taliban on Tuesday last week announced the start of their spring offensive, even as the government tries to bring them back to the negotiating table to end the drawn-out conflict.

The insurgents warned they would "employ large-scale attacks on enemy positions across the country" during the offensive -- dubbed Operation Omari in honour of the movement's late founder Mullah Omar, whose death was announced last year.

The Taliban's resurgence has raised serious questions about the ability of Afghan forces to hold their own and prompted calls for the US to reconsider its troop withdrawal schedule, already delayed once by President Barack Obama.

There are currently 9,800 American troops in the country, set to fall to 5,500 by 2017.

Peace talks which began last summer were abruptly halted after it was revealed that Mullah Omar had been dead for two years, a disclosure which sparked infighting in the insurgents' ranks.

A four-country group comprising Afghanistan, the United States, China and Pakistan has been holding meetings since January aimed at jump-starting negotiations, though their efforts have so far been in vain.

Afghan Chief Executive Abdullah Abdullah on Tuesday announced he was postponing his upcoming trip to Pakistan after "initial evidence of today's suicide attack".

Kabul has fraught relations with Islamabad, which it blames for sponsoring the insurgency.