A militant Islamist group has warned tourists to leave Egypt and threatened to attack any who stay in the country after tomorrow, raising the prospect of a new front in a fast-growing insurgency.

The Sinai-based Ansar Bayt al Maqdis group, which claimed responsibility for a suicide bombing that killed two South Korean tourists and an Egyptian on Sunday, made the statement on Twitter.

Islamist militants have killed hundreds of policemen and soldiers since the army deposed Islamist president Mohamed Mursi in July, but Sunday's attack on a tourist bus marks a strategic shift to soft targets that could devastate an economy already reeling from political turmoil.

The uprising that toppled Hosni Mubarak in 2011 scared off many tourists, dealing a major blow to an industry that accounted for more than 10% of Egypt's gross domestic product.