SEOUL (AFP) - South Korea voiced shock and outrage on Monday at the bombing of a tourist bus in Egypt that killed three of its nationals.

The bomb tore through the bus carrying 31 South Korean tourists and two South Korean guides near an Egyptian border crossing with Israel in South Sinai on Sunday.

"We are shocked and enraged at the terrorist bombing on the bus... and strongly condemn the act," Seoul's foreign ministry said in a statement.

Three South Koreans - two men and a woman - were killed along with the Egyptian driver, the ministry confirmed.

Another 14 were injured.

The tourists were all members of the same church group from the central South Korean county of Jincheon who were on a 12-day trip through Turkey, Egypt and Israel.

"We believe that terrorism can never be justified under any circumstances and such inhumane and unethical acts should be weeded out by all means," the ministry said.

The South Korean ambassador to Egypt, Kim Young So, told Seoul's MBN TV station that the bombing appeared to be a suicide attack.

"An Egyptian man in his 20s suddenly boarded the bus and detonated the bomb... it appears to be a suicide bombing by a terrorist," Kim said.

The foreign ministry said a high-level travel warning had been issued for the Sinai region and the Gulf of Aqaba, while nationals living elsewhere in Egypt were urged to take extra precautions.

A foreign ministry official had previously stated that the advisory amounted to a complete travel ban.

It was the first attack on tourists since the ouster of Islamist president Mohamed Morsi by the army in July sparked civil unrest and a spate of attacks across Egypt that have mainly targeted security forces.

The bomb exploded in the front part of the bus at the Taba border crossing with Israel, Cairo's interior ministry said.

The tourists had set off from Cairo and were waiting at the crossing to enter Israel when the explosion happened, it said.

No one immediately claimed responsibility for the attack.