Taliban militants on Thursday claimed a deadly attack on a bus transporting trainee policemen to Afghanistan's capital, Kabul.

The militant group's spokesman Zabihullah Mujahid said "many were killed and wounded" in what he described as a suicide attack.

At least 27 cadets were killed and 40 others injured, according to Afghan officials.

"We are still investigating the precise nature of the blast, whether it was a suicide attack, car bomb or whatever - we do not know at the moment," an unnamed senior interior ministry official told AFP news agency.

NATO's Resolute Support mission immediately condemned the attack, offering its "deepest condolences to the families of those killed and wounded."

"Resolute Support strongly condemns the suicide attack in Kabul today. The Taliban continue to display a total disregard for human life," the mission said on Twitter.

Last week, 14 Nepali security guards were killed en route to the Canadian embassy, where they worked, prompting Kathmandu to ban its citizens from working in the conflict-ridden country.

The Taliban has stepped up its attacks against Western-backed government targets after the ascension of Mullah Haibatullah Akhundzada.

In May, a US drone attack inside Pakistan killed Akhundzada's predecessor, ex-Taliban chief Mullah Akhtar Mansour.

ls/ (AFP, Reuters, AP, dpa)