It was first attack on tourists since the ouster of Islamist president Mohammed Morsi in July sparked unrest and a spate of attacks across the country.
 

The bomb went off in the front section of bus carrying the tourists at Taba border crossing with Israel in south Sinai, the interior ministry said, adding that one of those killed was the Egyptian driver.
 

Health ministry spokesman Ahmed Kamel told Agence France Presse four people were killed in the explosion and 13 were injured.
 

The bomb peeled off the front of the yellow bus and tore out parts of the roof.
 

A witness who had been waiting for a bus nearby described scenes of horror as the bomb ripped through the vehicle.
 

"There were body parts and corpses. I saw the corpse of a man who appeared to be Korean, with a leg missing," said the witness, Ahmed Ali, a doctor who runs a clinic in a neighboring resort.
 

The interior ministry said in a statement the tourists had set off from Cairo and were waiting at the crossing to enter Israel when the explosion took place.
 

A spokesman for the Israel Airports Authority, which is responsible for border security, told AFP that the Taba crossing had been closed in the wake of the blast.
 

No one immediately claimed responsibility for the attack.
 

Scores of policemen and soldiers have been killed in bombings in Sinai and the Nile Delta, but Sunday's attack was the first targeting tourists since Morsi was deposed.
 

The unrest has severely hit tourism, a vital earner in Egypt, which has been targeted sporadically by militants over the past two decades.
 

The government's census agency said the number of tourists was down in December 2013 by almost 31 percent compared with the same month in 2012.
 

Sunday's bombing came as a court in Cairo opened the trial of Morsi and 35 co-defendants on charges of espionage and collusion with militants to carry out attacks in Egypt.
 

The military-installed government has accused Morsi's Muslim Brotherhood of masterminding the attacks that have also targeted police headquarters in Cairo.
 

The Brotherhood, now designated as a terrorist group, denies its involvement in the bombings.
 

The deadliest attacks have been claimed by the Sinai-based Ansar Beit al-Maqdis group, whose leadership is drawn from militant Bedouin who want an Islamist state in the peninsula.
 

The group also took responsibility for downing a military helicopter in Sinai on Jan. 25 using a heat-seeking, shoulder-fired missile.
 

That attack prompted concerns that militants could use such weapons to target commercial flights to resorts in south Sinai.
 

Between 2004 and 2006, scores of Egyptians and foreign tourists were killed in a spate of bombings in resorts in south Sinai.  
 

In Cairo, a French tourist was killed in a 2009 bombing at the historic Khan al-Khalil bazaar, which police at the time blamed on militants from the neighboring Palestinian Gaza Strip.

In 1997, Islamist militants massacred dozens of tourists in a pharaonic temple in the southern city of Luxor.