At least 20 people have been killed and 70 wounded in separate blasts at a Kabul wrestling club.

An hour after a suicide bomber blew himself up at a sports hall in a heavily Shia neighbourhood on Wednesday, a car packed with explosives detonated as journalists and security forces gathered at the scene, police said.

Tolo News, Afghanistan’s largest private broadcaster, said two of its journalists were killed in the attack. The media support group NAI said at least four journalists were wounded in the second explosion.

There was no immediate claim of responsibility for the bombings. Islamic State often targets Afghanistan’s minority Shia population.

The Afghan president, Ashraf Ghani, said in a statement: “An attack on civilians and media workers of the country is an attack on freedom of speech and a crime against humanity.”

Pahlawan Shir, the director of the wrestling club, said: “I was outside when the first explosion happened, which has killed over 30 people, many of them wrestlers. I was searching for my coach, I have finally found him in the … hospital. He is in a critical condition.”

A spokesman for the interior ministry said at least 20 people were killed. An Afghan security source confirmed the numbers.

People who claimed to have witnessed the attack said the bomber killed the guards at the club before blowing himself up inside.

The bomber “detonated inside where a large number of athletes had gathered. There are a lot of dead and wounded,” Mohammad Hanif said on Facebook.

It was the deadliest on Kabul’s Shia population since 15 August, when a suicide bomber blew himself up in an education centre, killing dozens of students. Isis said it was behind that attack, which drew international condemnation. Most of the victims were studying for college entrance exams when the bomb went off.

Civilians have long borne the brunt of the violence in Afghanistan, especially in Kabul, a target of both the Taliban and Isis. Journalists have also paid a heavy price covering the conflict. Nine journalists and 16 other people were killed in twin explosions in Kabul on 30 April.

On Tuesday the Taliban announced the death of Jalaluddin Haqqani, who founded the eponymous militant group widely suspected of being behind some of the attacks in Kabul claimed by Isis.