Egyptian Prime Minister Hazem Beblawi has said Islamist militants in the Sinai peninsula are becoming a threat to foreign tourists, state TV reports.
Officials say they are taking seriously a reported ultimatum by Islamist militant group Ansar Beit al-Maqdis for tourists to leave the country.
The threat was reportedly made on a private Twitter account affiliated with the group, according to Reuters.
The Egyptian government has struggled against rising militancy in the Sinai.
The Twitter message gave all tourists until Thursday to leave Egypt or face attacks.
Ansar Beit al-Maqdis has denied using social media, but Reuters says the account has spoken for the group in the past.
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 Islamist group earlier claimed in an official statement that it was responsible for a deadly attack on a tourist bus on Sunday. Three South Koreans and an Egyptian were killed in the attack.
The al-Qaeda-inspired militant organisation, whose name means "Champions of Jerusalem", has increasingly turned its attacks against the Egyptian police and army.
The Sinai peninsula has become increasingly lawless since President Hosni Mubarak was overthrown in 2011.
Militants further stepped up their attacks after President Mohammed Morsi was ousted by the army last year.