Gunmen wearing police uniforms have kidnapped an American and an Australian in the heart of Kabul, the latest in a series of abductions of foreigners in Afghanistan.

The two professors at the American University of Afghanistan were seized from their vehicle on Sunday evening, officials said on Monday, as the kidnappers smashed the passenger window and hauled them away at gunpoint.

No group has so far claimed responsibility for the abductions, which came three days after a group of foreign tourists were ambushed by the Taliban in western Herat province, underscoring growing insecurity in Afghanistan.

"Two foreign professors, one American and the other Australian, were abducted at gunpoint from Dar-ul-Aman road in the centre of Kabul city," Sediq Sediqqi, interior ministry spokesman, told the AFP news agency.

"Indications are that they were kidnapped by a criminal group."

The driver and a guard inside the vehicle, both unharmed, have been held for questioning, another security official told AFP.

Four gunmen wearing police uniforms were involved in the abduction, according to a Western official in Kabul.

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The Afghan capital is inundated with organised criminal gangs who stage kidnappings for ransom, often targeting foreigners and wealthy Afghans, and sometimes handing them over to armed groups.

“[There is] very high concern here about the security situation, and not just for foreigners … Afghans too are suffering from kidnapping, and it’s really because the economy is so bad … there are not enough jobs and so people have turned to crime,” Al Jazeera’s Jennifer Glasse, reporting from Kabul, said.

“It’s a real concern for people in Kabul and around the country because kidnapping has become a lucrative business.”

The US State Department said that it was aware of reports of the kidnapping of an American but declined to comment further.

The Australian government confirmed the "apparent kidnapping" of one of its citizens, citing its embassy in Kabul, but also refused to elaborate due to security considerations.

"We continue to advise Australians not to travel to Afghanistan because of the extremely dangerous security situation, including the serious threat of kidnapping," the government said in a statement.

Growing insecurity

The abductions, the fourth this year, highlight the growing dangers faced by foreigners in Afghanistan.

Foreign tourists, including British, American and German nationals, came under Taliban fire last week in a volatile district of Herat, leaving some of them wounded. They were safely evacuated to Kabul and were flown out of the country.

Aid workers in particular have increasingly been casualties of a surge in militant violence in recent years.

Judith D'Souza, a 40-year-old Indian employee of the Aga Khan Foundation, a prominent NGO that has long worked in Afghanistan, was rescued last month after she was abducted near her residence in the heart of Kabul on the night of June 9.

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D'Souza's abduction came after Katherine Jane Wilson, a well-known Australian NGO worker, was kidnapped on April 28 in the city of Jalalabad, close to the border with Pakistan.

Wilson, said to be aged 60, ran an organisation known as Zardozi, which promotes the work of Afghan artisans, particularly women.

The United States in May warned its citizens in Afghanistan of a "very high" kidnapping risk after an American narrowly escaped abduction in the heart of Kabul.

In April last year the bullet-riddled bodies of five Afghan workers for Save the Children were found after they were abducted by gunmen in the strife-torn southern province of Uruzgan.

Roadside bombs

Meanwhile, two separate roadside mine blasts killed eight civilians in Afghanistan on Monday, officials said.

One mine detonated as a rickshaw carrying a family in Gilan district of southern Ghazni province passed by, killing six members of one family, said Fahim Amiri, spokesman for Ghazni's governor.

"Three women, two children and a man were among the killed."

The area is under Taliban control, although Afghan security forces are trying to push the group out.

"That is why the Taliban are planting mines on the roads. They are targeting vehicles of the security forces," Amiri said.

Another mine hit an Afghan National Army (ANA) vehicle in the Bagrami district of Kabul, "killing two civilians and wounding another two, including a ANA solder," said Basir Mujahid, Kabul police spokesman.

Bagrami district in eastern Kabul is known as one of the most insecure districts of the capital.

The United Nations regularly criticises the Taliban for the use of IEDs planted by roadsides as they are indiscriminately killing hundreds of civilians every year.