Kabul (AFP) - Thirty people were killed and hundreds wounded when a Taliban truck bomb tore through central Kabul and a fierce firefight broke out Tuesday, one week after the insurgents launched their annual spring offensive.
The Taliban claimed responsibility for the attack in a densely crowded neighbourhood, which sent clouds of acrid smoke billowing into the sky and rattled windows several kilometres (miles) away.
The brazen assault near the defence ministry marks the first major Taliban attack in the Afghan capital since the insurgents announced the start of this year's fighting season.
"One of the suicide attackers blew up an explosives-laden truck in a public parking lot next to a government building," Kabul police chief Abdul Rahman Rahimi told reporters.
"The second attacker engaged security forces in a gunbattle before being gunned down."
Interior ministry spokesman Sediq Sediqqi said 30 people, including women and children, were killed in the attack on a government office that provides security to senior officials.
He added that more than 320 people were wounded, with many of them battling for their lives in hospital -- an indication that the death toll could rise.
"I saw wounded people lying on the road and screaming helplessly," said Sadiqullah, who runs a tea stall near the building which was attacked.
"We are fed up with such attacks. How long must ordinary civilians suffer like this?"
The interior ministry said hundreds of kilograms of explosives were used in the bombing, the deadliest so far this year in the Afghan capital.
The scene of the attack was littered with upturned cars, many of them mangled and charred.
The pitched firefight appeared to die down several hours after the powerful explosion, but some security officials expressed concern that other bombers may still be on the loose.
The Taliban claimed three "martyrdom seekers" carried out an attack on the National Directorate of Security, the main spy agency. One of them, it said, managed to slip away alive.
The NDS says it had used the building in the past.
Later Tuesday, a second explosion was heard in downtown Kabul, but the nature of the blast was not immediately clear and no casualties were reported.
- 'War crimes' -
"This (deadly) attack shows the devastation caused by the use of explosive devices in urban areas and once more demonstrates complete disregard for the lives of Afghan civilians," the UN said.
"The use of explosives in populated areas, in circumstances almost certain to cause immense suffering to civilians, may amount to war crimes."
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 began the fighting season last week by targeting the northern city of Kunduz, which they briefly captured last year in a stunning setback for Afghan forces.
But officials said Afghan security forces drove Taliban fighters back from the city on Friday.
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.
The US State Department condemned Tuesday's attack, saying the violence only deepened its support for the government.
"The United States condemns in the strongest terms the attack today in Kabul," spokesman John Kirby said.
"Attacks like these only deepen our support for the people and government of Afghanistan, and their efforts to bring security and stability to Afghanistan."
Afghan Chief Executive Abdullah Abdullah 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.