A co-ordinated double suicide bombing hit central Kabul on Monday morning, killing 25 people.
Eight journalists were among the dead, including an AFP photographer and a cameraman for a local TV station, as well as four police officers, Afghan officials said.
At least 45 other people were injured.
In a statement posted on an Islamic State-affiliated website, the group said two of its members had carried out the bombings, targeting the headquarters of the “renegade” Afghan intelligence services.
A few hours later a suicide car bombing in Kandahar killed 11 children, police in the southern province said.
Police spokesman Hashmat Stanekzai said the first suicide bomber in Kabul was on a motorbike while the second attacker was among the crowd of reporters who rushed to the scene of the first attack, pretending to be one of the media.
He added that the second attacker then detonated his explosives while still among the reporters.
Agence France-Presse reported that the news agency’s chief photographer in Kabul, Shah Marai, was among those killed.
AFP said Marai died in the second blast which targeted a group of journalists who had rushed to the scene of the earlier suicide attack in the capital.
A local media watchdog, the Afghan Journalists Safety Committee, said eight Afghan journalists were killed and six were wounded.
Sediqullah Tawhidi, an official from the committee, said a cameraman form the local Tolo TV also was among those killed.
Police officer Jan Agha said all the journalists died in the second blast, which also wounded two police officers.
The suicide attacks took place in the central Shash Darak area, which is home to the Nato headquarters and a number of embassies in Afghanistan.
The second was meant to hit those rushing to the scene of the attack to help the victims of the first blast.
Kabul chief of police Dawood Amin said the area of Kabul that was targeted, which includes many foreign offices, was quickly sealed off.
In the Kandahar attack, an official said a suicide bomber targeted a Nato convoy in the district of Daman but killed 11 children from a religious school near the site of the blast.
Matiullah Helal, deputy spokesman for the provincial police chief, said 16 people were also wounded, including five Nato soldiers, nine civilians and two policemen. There was no immediate claim of responsibility for the Kandahar bombing and no comment from Nato.
The children from the madrasa had gathered around the convoy when the bomber struck, one witness said.
The local Islamic State group affiliate and the more firmly established Taliban carry out regular attacks around the country, with the Taliban usually targeting the government and security forces and IS targeting the Shiite minority.
Large-scale attacks by the two militant groups have also hit the Afghan capital. Both groups want to establish strict Islamic rule in Afghanistan.