An explosion ripped through a tourist bus near Egypt's border with Israel killing three South Korean tourists and their Egyptian driver.
The bus, carrying 33 tourists, was travelling from St. Catherine's Monastery, in central Sinai, to Israel, when it exploded at the border crossing in Taba.
The South Korean foreign ministryexpressed the country's "utmost resentment and outrage" as it "strongly condemned" the attack that also seriously wounded 12 people.
Security officials say the cause of the explosion was not clear, but that it most likely was from a bomb in or near the vehicle.
Islamist militants, based in the Sinai peninsula, have increased attacks on security forces since the overthrow of former president Mohamed Morsi in July.