A senior police officer said they arrested a tour guide, a driver, a cleaner and a hotel staff. He, however, refused to reveal the names of the four as police will first conduct a test identification parade.
The arrest came on a day when the Delhi Commission for Women (DCW) issued a notice to Delhi Police asking them why the Rape Crisis Cell of the women's panel was not informed when the victim's statement was recorded.
In her complaint, the US national had alleged that she was raped by five persons in a five-star hotel in April. Police are on a lookout for the fifth accused as the woman has not shared details about him, said the officer.
They were being questioned extensively following the registration of an FIR on December 3.
They will be produced in court tomorrow where their police custody will be sought for custodial interrogation to gain more evidence, he added.
The mobile phones of the accused have been seized by the police.
The court will have to sanction the Test Identification Parade and it will take some time, sources said.
The woman is likely to return to the US tomorrow and if the court grants permission to conduct identification parade, it might be done on Skype, they added.
Earlier, she had said that she was not "satisfied" with the probe and was ready to come to India to identify the accused.
On December 8, the tourist guide, accused of raping the woman, along with his accomplices, was questioned by police after his arrival from Nepal.
Police had identified the man and had contacted him while he was in Nepal.
The woman had alleged that she was raped by the men for two days. They also threatened her with dire consequences if she reported the matter to anybody.
A team of psychologists and psychiatrists have been assisting the lady in recalling the details of the incident. The team is also working with Delhi Police in their investigation to tie up loose ends.
"Though she is sad about the fact that there was a delay in registering the FIR and arresting them, she is positive that at least four persons have been arrested. She is hopeful that Delhi Police will do their best so that these people are convicted.
The sources also said the identification parade can be conducted tomorrow.
