Five men have been arrested in India charged with kidnapping and repeatedly raping a Japanese student.
Police in the eastern city of Calcutta say the assaults took place over a period of more than a month from 23 November and in at least two locations.
They say an organised gang is suspected of targeting single women tourists.
Increasing numbers of rape cases are being reported and highlighted in India, prompting widespread outrage.
Pallav Kanti Ghosh, a Calcutta police commissioner, told BBC Hindi that two of the men - said to be brothers - approached the 23-year-old victim as tourist guides after she arrived in the city and checked into a hotel in an area popular with foreign tourists.
"One of the men spoke very fluent Japanese," he said.
"They said: 'We are guides and want to take you sight-seeing.'
"They took her to Digha [a beach resort in West Bengal state] on 23 November. There they sexually assaulted her and robbed her of 76,000 rupees [£1,200] using her ATM card."
She was then taken to Bodh Gaya, the holiest site of Buddhism and a major pilgrimage and tourist centre.
"There, the men handed her over to other gang members," Mr Ghosh said.
The woman was held captive for several weeks and the assaults continued, he said.
In late December she managed to reach the city of Varanasi from where she travelled to Calcutta, lodging a complaint via the Japanese consulate on 26 December.
Mr Ghosh said three of the men were arrested near Bodh Gaya and two in Calcutta. The Hindustan Times newspaper said some were held after their mobile phone calls were intercepted.
He said police were searching for other members of what he called an organised gang, several of whom are reportedly proficient in Japanese.
Sexual violence in India has been in the spotlight since a student was fatally gang-raped on a bus in Delhi two years ago.
That and other cases have prompted a domestic and international outcry.
Other foreign women targeted by gang-rapists include a Swiss cyclist assaulted in central India in 2013 and a Danish tourist attacked in Delhi a year ago.
Rape laws have been toughened in response to the crimes but correspondents say this has failed to act as a deterrent.