Two separate suicide bombs killed more than 20 people in Afghanistan on Monday as the Taliban continued its insurgency against the Western-backed Kabul government.

At least 14 Nepalese workers died when a suicide attack hit a bus as they travelled to work in the Afghan capital. A separate explosion hours later in a crowded market in the northern Badakhshan province killed at least eight and wounded another 18. The casualty count could rise.

The Taliban has claimed responsibility for the attack in Kabul which is the first since the Islamic holy month of Ramadan began.

Sediq Sediqqi, a spokesman for the interior ministry, said the bomber had waited for the bus to emerge from a housing compound where the Nepalese security contractors lived. They were employed by the Canadian embassy through a private security firm.

The Nepalese government said they were still confirming the attack but Indian Prime Minister Modi tweeted his condolences.

No group has claimed responsibility for the attack in Badakhshan.

The blasts follow a deadly suicide attack on a bus carrying justice ministry staff near Kabul last month and a separate attack on a court in the central city of Ghazni on June 1.

The Taliban claimed both those attacks in revenge for the execution of six Taliban prisoners.

Last month former Taliban leader Mullah Akhtar Mansour was killed in a US drone strikeand was replaced by Mullah Haibatullah Akhundzada. The recent bomb attacks indicate the change in leadership will not provide let-up for Afghanistan's beleaguered government who is struggling to cope as the US gradually withdraws its troops.

Additional reporting by Reuters.