The Egyptian government has told the BBC that it is taking seriously an alleged 48-hour ultimatum by Islamist militant group Ansar Beit al-Maqdis calling on all tourists to leave Egypt.
The threat was reportedly made on a private twitter account "affiliated with" the group, according to Reuters.
The group has denied having any social media accounts, but Reuters claims the account has been accurate in the past.
The Egypt government has struggled against rising militancy in the Sinai.
A spokeswoman at the Egyptian embassy in London said that while the government could not be sure of the authenticity of the threat, "extra precautions have been taken in recent days to protect tourists in the resort area of Sharm El Sheikh".
The group earlier claimed in an official statement that it was responsible for a deadly attack on a tourist bus on Sunday.