The kidnapping followed warnings from security agencies that foreigners might be targeted in response to the arrest of a suspect in the kidnappings of three UN election workers last year.
A group of "thieves" claimed responsibility for the abduction of aid worker Clementina Cantoni, 32, said Gen. Jamil Jumbesh, head of the Interior Ministry's anti-terror division. He declined to say whether the group had made demands or give other details.
"Four men carrying Kalashnikovs bashed in the window of her car and took her away. They told the driver not to move or he would be shot," said CARE's director, Paul Barker.
The driver had just dropped a Canadian former CARE employee at a house in Kabul's downtown Shahr-e-Naw district when the kidnappers driving a sedan cut off the vehicle and abducted the Italian at about 8:30 p.m., Barker said. The kidnappers then drove toward a nearby Christian cemetery, he said.
Afghan authorities, including President Hamid Karzai, were quickly alerted to the kidnapping after the Canadian woman made a panicked call to Barker, the director said. She made it safely into the house but heard the attackers banging on the car, he said.
Marco Formigoni, a family friend, spoke to reporters outside the Cantoni family home in an upscale Milan neighborhood, relaying the family's hope "that this affair ends quickly and well."
Security forces manning checkpoints through the night found no trace of Cantoni, Gen. Mahboubullah Amiri, a police commander in the Afghan Interior Ministry, said Tuesday.
"They are searching cars and asking the drivers for their documents, but there are no positive signs so far," Amiri said.
It was the second kidnapping of a CARE worker by suspected militants in recent months. Margaret Hassan, the British director of CARE International in Iraq, was kidnapped in Baghdad in October and believed killed, although no body was recovered.
In Kabul, security forces immediately sealed off all main roads leading out of Kabul, said Jamil Khan, head of the criminal investigation department for the city's police. Officers stopped and searched cars in the city center, checking trunks and under seats.
"Police are trying very hard to produce some good news," Khan said. Cantoni has lived in Afghanistan since 2002, said CARE, one of the largest and most established international aid groups in the country. The organization issued a brief statement calling for her release.
In Rome, the Italian foreign ministry said a crisis unit that has handled past abductions of Italians abroad was working on the case, and that Foreign Minister Gianfranco Fini was following the situation.
Relations between the United States and Italy have been strained over the March 4 shooting death of Italian agent Nicola Calipari --who had just helped free an Italian hostage -- by US soldiers at a checkpoint in Baghdad.
The abduction follows a string of warnings to the roughly 3,000 foreigners living in Kabul that they could be targeted in attacks, including kidnappings.
On May 7, a suicide bomber blew himself up in an Internet cafe in the same area as Monday's abduction, killing a U.N. worker from Myanmar. Last month, an American civilian was briefly abducted in Kabul but escaped by throwing himself from a moving car.
Kabul had been largely free of the fear of the kind of kidnappings rife in Iraq until October, when three U.N. election workers -- one each from the Philippines, Northern Ireland and Kosovo --were seized at gunpoint in the city. They were released unharmed a month later.
A Taliban splinter group claimed responsibility for the kidnapping, though officials and diplomats have suggested criminals --possibly working for factions that oppose the growing authority of the US-backed government -- were responsible.
