At least 20 people have been killed including two Afghan journalists after twin blasts at a Kabul wrestling club on Wednesday that left another 70 wounded, officials said, in the latest deadly assault on the capital.

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

At least four journalists were wounded in the second explosion, media support group NAI said.

Tolo News, Afghanistan's largest private broadcaster, confirmed two of their journalists were killed.

The Islamic State group claimed responsibility for the twin explosions, the US-based SITE intelligence group reported, citing the IS propaganda channel Amaq. IS often targets Afghanistan's minority Shiite community. The Taliban denied involvement in a WhatsApp message to journalists.

"An attack on civilians and media workers of the country is an attack on freedom of speech and crime against humanity," Afghan President Ashraf Ghani said in a statement condemning the latest violence.

A spokesman at the interior ministry said at least 20 people were killed and another 70 wounded in the blasts. An Afghan security source confirmed the casualty toll.

Civilians and members of the security forces also were among the dead and wounded.

Health ministry spokesman Wahid Majroh put the death toll at 16 people and another 87 wounded.

"I was outside when the first explosion happened, which has killed over 30 people, many of them wrestlers," Pahlawan Shir, director of the Maiwand wrestling club, told AFP.

"I was searching for my coach, I have finally found him in the... hospital. He is in a critical condition." Social media users who purportedly witnessed the attack said the bomber killed the guards at the club before blowing himself up inside.

He "detonated inside where a large number of athletes had gathered. There are a lot of dead and wounded", Mohammad Hanif said on Facebook.

A photo posted on Twitter purportedly showed several victims being loaded into the back of a police pick-up.

Tolo News reporter Samim Faramarz, 28, and camerman Ramiz Ahmadi, 23, had been doing a live report from the scene moments before the second blast.

The two men were "committed to the future of the country and they had big dreams for their future", Tolo News director Lotfullah Najafizada said in a statement paying tribute to the pair.

Across the country, two consecutive explosions near a police checkpoint in Herat city wounded three civilians and two police officers, Herat police spokesman Abdul Ahad Walizada told AFP.

The last major attack on Shiites in Kabul was on August 15 when a suicide bomber blew himself up in an education centre, killing dozens of students.

IS said it was behind that attack, which drew international condemnation and came amid a wave of deadly violence across the country.

Most of the victims were studying for college entrance exams when the blast happened.

Civilians have long borne the brunt of the violence in Afghanistan -- especially in Kabul, a target of both the Taliban and IS.

Journalists also have paid a heavy price covering the conflict. At least 11 were killed in the first six months of the year, the Afghan Journalists Safety Committee said in a report, describing the period as the "bloodiest".

On April 30, twin explosions in Kabul killed nine journalists and 16 other people. Among the dead was AFP chief photographer Shah Marai.

AFP driver Mohammad Akhtar was killed less than three months later in a suicide attack in Kabul that also claimed the lives of 22 others.

Wednesday's attack comes a day after the Taliban announced the death of Jalaluddin Haqqani, who founded the eponymous militant group which is widely suspected of being behind some of the attacks in Kabul claimed by IS.

Afghan special forces arrested 11 Haqqani militants in Kabul and nearby districts, the country's intelligence agency said Wednesday.

The Taliban has been conducting blistering attacks on security forces across Afghanistan, including the massive, days-long onslaught on the eastern city of Ghazni last month.