A suicide bomber blew himself up in a crowd of protesters in the eastern Afghanistan province of Khost on Thursday, killing 18 and wounding scores more, Afghan government officials said.

The assault unfolded around 10 a.m. as the demonstrators gathered to protest the policies of the province’s governor, said Mobarez Zadran, a spokesman for the governor’s office. The bomber, Zadran said, waded into the gathering and detonated his explosives.

Among the wounded was a prominent Afghan lawmaker, Humayoon Humayoon, who was one the event’s organizers. The protests had been going on for several days.

In a tweet, President Ashraf Ghani’s office condemned the attack, describing it as “an unforgivable crime against innocent civilians.”

Afghan firefighters try to extinguish fire at the site of a suicide bomb blast in the Khost province on Thursday. (Ahmadullah Ahmadi/European Pressphoto Agency)

While suspicion immediately fell on the Taliban, its spokesman Zabihullah Mujahid denied responsibility for the attack, also in a tweet.

Thursday’s attack was the latest sign that violence is escalating again after a nearly three-month winter lull, traditionally a period when the war subsides. Last week, a suicide bomber killed seven and wounded 36, striking close to the presidential palace and finance ministry in the Afghan capital. Prior to that, another suicide bomber killed a powerful regional police commander in the capital.

Thursday’s bombing was the first major assault since Ghani, and his chief executive Abdullah Abdullah, returned from a visit to meet President Obama and other officials in Washington and New York. Ghani secured a commitment from President Obama to slow the planned exit of 9,800 U.S. troops from Afghanistan amid concerns that the Taliban and other militants could launch heavy offensives during the spring and summer.

As most U.S. and international forces have left, casualties have mounted for Afghanistan security forces, which are struggling against a still potent Taliban, with last year being the worst on record. More than 10,000 Afghan civilians also died or were injured in the conflict last year, the largest number since the United Nations started keeping records in the country.

Mohammad Sharif contributed to this story.