Four men have been arrested in India's capital New Delhi on suspicion of raping an American tourist in April, police said.

The 25-year-old woman lodged a complaint in October and recently returned to India to testify before a magistrate and identify the accused, according to the Times of India.

Deependra Pathak, joint commissioner of Delhi Police, told Reuters: "We are interrogating four persons while the fifth accused still has to be identified and arrested."

He added that the four suspects include a tour guide, a driver, a cleaner and a hotel employee. The victim left India after the incident and she only started to remember the incident towards the end of July, he said.

The four men were arrested after the police received a complaint from a charity organisation based in the US on behalf of the victim, which was followed by the woman's written statement earlier this month in which she said five people drugged her and sexually assaulted her over two days.

The woman, who will go back to the US on Tuesday (27 December) evening, she said the arrests were a positive step.

Police said they were not arrested earlier because there was no evidence. On 5 December, they were identified and questioned.

Last month, a Japanese tourist was assaulted in south India. Five men were jailed for life in June for gang-raping a 52-year-old Danish woman in 2014 in Delhi.

According to statistics released by India's National Crime Record Bureau, over 34,000 cases of rape were reported in 2015 countrywide. In the wake of the fatal gang rape of Jyoti Singh in December 2012 in Delhi, tough laws were introduced against sex offenders.