A suicide bomber killed at least 16 people Thursday and wounded 40 others, including a prominent lawmaker, at an anti-corruption rally in eastern Afghanistan, the latest casualties ahead of the Taliban's expected spring offensive.

The attack comes just a week after Washington announced it would not be halving the 9,800 US troops still in Afghanistan by the end of the year, backpedalling on previous plans.

The Taliban, waging a deadly insurgency since they were ousted from power in late 2001, warned that the US troop announcement would damage any prospects of peace talks as they vowed to continue fighting.

Thursday's attack targeted an anti-graft demonstration outside the residence of the acting governor of restive Khost province, sending terrified, blood-soaked victims fleeing for cover.

Severed limbs and body parts lay strewn around the area after the powerful blast, according to an AFP reporter at the scene.

The area was cordoned off by security officials as yellow-helmeted firefighters used water hoses to douse the smouldering scene of the explosion.

"Today morning, a suicide attack was carried out by the enemies of peace and stability of Afghanistan at a rally in the city of Khost, in which 16 people were martyred, and 40 others were wounded," said Abduljabar Naeemi, the acting governor of Khost province, which borders Pakistan.

Humayoun Humayoun, a well-known MP from Khost province, was among those wounded, Naeemi added in his statement.

The interior ministry in Kabul said 17 civilians were killed and 37 others were wounded in the explosion, adding that it "strongly condemns the terrorist attack".

President Ashraf Ghani also condemned the "cowardly attack during a peaceful protest -- which is the civil right of our people".

Protesters accusing Naeemi of rampant corruption and land grabbing have staged demonstrations outside his residence for nearly a week.

The Taliban denied responsibility for the blast, spokesman Zabihullah Mujahid said on the group's official Twitter account, but suicide bombings have long been a weapon of choice for the militants in their 13-year battle against the government and its foreign backers.

The bombs often target Afghan security forces, but they have also taken a heavy toll on civilians.

The number of civilians killed and wounded in Afghanistan jumped 22 percent in 2014, a recent UN report said, as NATO troops withdrew from combat.

The United Nations Assistance Mission in Afghanistan attributed the rise to an intensification in ground fighting, resulting in a total of 10,548 civilian casualties last year.

It condemned Thursday's blast, saying "such an attack deliberately targeting... civilians is an atrocity".

President Barack Obama last week reversed plans to withdraw around 5,000 US troops from Afghanistan this year, an overture to the country's new reform-minded leader, President Ashraf Ghani.

A large section of Afghan society welcomed the decision, with many fearing that without continued international military support, Afghanistan -- like Iraq -- could spiral into chaos.

Afghan forces are bracing for what is expected to be a bloody summer push by the Taliban and the government has also raised the ominous prospect of the Islamic State jihadist group making inroads into Afghanistan.

Taliban insurgents have already stepped up suicide attacks on government targets following an Afghan army offensive which began in southern Helmand province more than two months ago.

A roadside bomb killed Hekmatullah Haqmal, the police chief of Gereshk district of opium-rich Helmand late Wednesday, according to local officials.

He was part of a convoy of reinforcements heading to a village to launch a retaliatory attack against Taliban insurgents after they raided police checkpoints.

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