Hotel staff confirmed they were found with white froth coming from their mouths. The hotel has handed over closed-circuit TV footage, and police are continuing interviews with staff who dealt with the men.

Police said the men checked in after arriving in Hong Kong on October 10.

One was found slumped partially on a chair and the floor, and the other was on a bed. There were no signs of injuries, ransacking or fighting.

A police spokeswoman said the case was still classified as a 'dead body found' while investigations continue. An initial postmortem examination was inconclusive.

The spokeswoman refused to confirm reports the men were seen arriving at the hotel with two women, saying 'all options' were being considered.

Police sources said they feared the case could be an attempted robbery gone wrong, perhaps using the 'date rape' drug flunitrazepam, often sold as Rohypnol.

There have been a number of incidents in recent years of men reporting to police the theft of money from accounts with no recollection of how it happened.

Most only remember drinking at bars in the Wan Chai entertainment district.

The same drug was a factor in the January 8, 2003 death of Kari Juhani Koivuniemi, 45, a chief superintendent of the Ministry of the Interior Police Department of Finland. He suffered a heart attack at the Island Shangri-la. Police investigated the case as a murder, but it was apparently never solved.

Koivuniemi, an official guest of the Immigration Department, was last seen with an unidentified Asian woman, believed to be a mainland prostitute. Security camera footage showed the officer returning to the hotel at 5.48am.

The US consulate would not comment or give further information about the two men.