Afghan investigators inspect the site of a suicide bomb attack in Herat province on Tuesday. (AREF KARIMI/AFP/GETTY IMAGES)

At least 18 people, including police and civilians, were killed in attacks in Afghanistan on Tuesday, a spate of violence that coincided with the start of the country’s traditional fighting season.

The first incident, a suicide blast, occurred during morning rush hour on a road near the airport in the western city of Herat, a police chief, Sayed Agha Saqib, said. Eleven people were killed.

Hours later, three suicide bombers armed with guns stormed the main police station in Musa Qala, in the southern province of Helmand, according to provincial spokesman Dawoud Ahmadi. Four police officers were killed in an initial round of gunfire at the entrance of the compound and by the blasts triggered by two bombers who managed to get inside, Ahmadi said. Five officers, including the district police chief, were wounded in the attack.

A fourth bomber, on a motorbike, killed three more officers by detonating his explosives near their car as they headed to help victims of the first bombings, Ahmadi said. Six people, three of them police, were injured in the latter blast.

In a statement posted on a Taliban Web site, the group asserted responsibility for the attacks in Musa Qala, but not the attack in Herat.

The insurgents have fought for more than a decade to drive foreign forces from Afghanistan and topple its government. After a pause during Afghanistan’s harsh winter, Taliban cells have unleashed a string of suicide attacks in various parts of the country in recent days.

In one such strike, three U.S. servicemen were killed in Faryab province, in the north, last week. The head of the government-run peace council for the eastern province of Konar, tasked with conducting negotiations with the insurgents, was killed in a similar attack Friday.

On Tuesday, in the Herat incident, two bombers — a woman wearing a burqa and her male driver — were seen traveling in a vehicle on the airport road. Security forces tried to stop them but failed, Saqib said. The pair, wearing explosive vests and carrying extra explosives in the car, blew themselves up after another group of security forces set up a human chain to block them, Saqib said by phone from Herat.

“We do not know what the target was,” he said. “Eight civilians and three police were killed in the explosion, and 22 other people were wounded.”

The explosion occurred near government buildings in the Guzara district, on a main road leading to Herat’s airport, where foreign troops are stationed. Herat is a relatively secure region, but Taliban bombers in the past have targeted foreign and Afghan forces in the province, mostly on the airport road.