Diplomats say they are helping a British and an Irish woman arrested in Peru over alleged drug trafficking offences.
Melissa Reid, 19, from the UK and Michaella McCollum Connolly, 20, from Belfast, were reportedly detained in Lima on Tuesday while trying to board a flight to Madrid.
McCollum Connolly's family had mounted an online campaign to find her last week after she went missing from Ibiza, where she was a dancer and hostess in a nightclub.
Her sister Samantha said that her "phone is off and her Facebook page has had no activity", which was out of character.
The pair are being questioned in connection with the discovery of more than 11kg of cocaine in food products in their luggage.
The Foreign Office in London confirmed it was helping a British national.
"We are aware of the arrest of a British national in Peru this week and are providing consular assistance," a spokeswoman said.
Ireland's Department of Foreign Affairs said it was also providing consular assistance to the family of an Irish woman being held in Peru on suspicion of drug trafficking offences.