KABUL — At least 12 people were killed, three of them children, and 20 others were wounded when a car bomb exploded near the Kabul airport early Wednesday, Afghan officials said, the first major attack on the Afghan capital after about a month of relative calm.

The suicide bombing came the day after President Ashraf Ghani said he would release three ­Taliban-affiliated insurgent commanders from prison. It was a major concession that Ghani said he hoped would jump-start talks and lead to the release of hostages, including two foreigners — one American and one Australian — who were kidnapped by the insurgents in 2016.

No group has publicly claimed responsibility for Wednesday’s attack. It was unclear whether the prisoners Ghani said would be released were still in custody Wednesday.

The three prisoners — Mali Khan, Hafiz Rashid and Anas Haqqani — belong to the Haqqani network, a violent group allied with the Taliban. The network has been behind the abductions of a number of high-profile foreigners in recent years, including U.S. soldier Bowe Bergdahl, who was held for five years.

Haqqani is the son of the Haqqani network’s founder. His older brother is the deputy leader of the Taliban.

The three prisoners were expected to be transferred to Qatar on Tuesday evening, according to an Afghan security official who spoke on the condition of anonymity because he was not authorized to speak publicly about the exchange. He said that the two hostages, U.S. citizen Kevin King, 63, and Australian Timothy Weeks, 50, had not yet been released but that the Afghan government hoped that transferring the Haqqani network commanders would lead to an exchange.

Ghani’s announcement about the exchange was a departure from his government’s past statements that releasing Haqqani would be a “red line,” and it comes at a politically sensitive time.

Results from a Sept. 28 presidential election that pitted Ghani against his political rival, Abdullah Abdullah, who is serving as Afghanistan’s chief executive, are pending. On Wednesday, the country’s election commission said the results would not be announced Thursday as planned.

The target of Wednesday’s blast appeared to be an armored vehicle belonging to GardaWorld, a Canadian security company, and at least four of the wounded were foreigners, said Nasrat Rahimi, a spokesman for the Interior Ministry. He did not know the nationalities of the wounded. GardaWorld said in an emailed statement that its employees were “impacted” in the attack but declined to comment further.

The powerful blast shook Kabul during rush hour, smashing windows of houses and shops nearby, residents said.

The deaths of at least three children in the attack added to a growing number of child casualties in Afghanistan. Last month, the United Nations said that between Jan. 1 and Sept. 30, at least 631 children were killed in Afghanistan and 1,830 were wounded, an 11 percent increase compared with the same nine-month period the previous year.

Sharif Hassan contributed to this report.