CAIRO -- An explosion tore through a bus filled with South Korean sightseers in the Sinai Peninsula on Sunday, killing at least four people and raising fears that Islamic militants have renewed a bloody campaign to wreck Egypt's tourism industry.
The bombing near the tip of the Red Sea's Gulf of Aqaba was the first attack against tourists in Sinai in nearly a decade.
There was no immediate claim of responsibility. But the blast bore the hallmarks of attacks blamed on the al-Qaida-linked militant groups that have been battling government forces in Sinai's restive north for years.
At least three South Korean tourists were killed and 12 more were seriously wounded, according to Egyptian security officials. The Egyptian bus driver was also among the dead, the officials said.
Egypt's vital tourism sector, which normally accounts for about 11 percent of the economy and 20 percent of all foreign currency revenue, has been badly hit by the deadly turmoil that has roiled the country since the 2011 revolt that overthrew ruler Hosni Mubarak.
Sunday's attack came as signs of a slow recovery in the industry were emerging, especially at Red Sea resorts in Sinai like Sharm el-Sheik.
"I am deeply saddened by the incident," Tourism Minister Hesham Zazou told state TV. The Egyptian presidency called the attack a "despicable act of cowardice" and vowed to bring the culprits to justice.
"The sad consequence for Egypt is that this takes the tourism industry and devastates it for years into the future," said Jon Alterman, director of the Middle East Program at the Center for Strategic and International Studies in Washington.
Egyptian security officials said they believe the blast was caused by either a car bomb or a roadside bomb that was detonated by remote control.
Rescue workers found the remains of four and perhaps five people, according to Khaled Abu Hashem, the head of ambulance services in southern Sinai.
In Seoul, the foreign ministry said in a text message that 31 passengers from a church in Jincheon were being led by a South Korean tour guide. Two of its citizens were killed and nine wounded, the ministry added.
The discrepancy in the death toll could not immediately be reconciled.
The attack stoked fears that a deadly campaign against tourists similar to one waged in the 1990s by extremists may have resumed. In 1997, gunmen opened fire at the Temple of Hatshepsut in the city of Luxor, killing 58 tourists and four Egyptians.
Sunday's bombing was the first attack against tourists in Sinai's southern region since a spasm of bloodshed in 2004-06 that killed about 120 people. That included a bombing at a luxury hotel in Taba in 2004 that left 34 people dead, 11 of them Israelis.
The bus in Sunday's attack had set out on a journey from Cairo and was about to enter Israel from the border town of Taba, officials said. Security officials said it arrived at Taba from the ancient Greek Orthodox monastery of St. Catherine's in Sinai.
The officials spoke on condition of anonymity because they were not authorized to speak to the media.
Meanwhile on Sunday, lawyers for deposed Islamist President Mohammed Morsi and his co-defendants walked out of court to protest the soundproof glass cage in which the accused are held during proceedings.
It was the first hearing in a case in which Morsi and 35 others are charged with conspiring with foreign groups and undermining national security.
The judge ordered Egypt's lawyers union to appoint 10 members to represent the defendants. The trial was adjourned until Feb. 23.
The soundproof cage was introduced after Morsi and his co-defendants interrupted other court cases by talking over the judge and chanting slogans.
The cage is fitted to give the judge sole control over whether the defendants can be heard.
In a separate development, the office of Egypt's former chief of staff, Sami Annan, announced Sunday that the retired general will run for president in elections slated for April.
The decision apparently pits Annan against Abdel-Fattah el-Sissi, the general who led the military takeover that ousted Morsi. El-Sissi is widely expected to announce his candidacy and is heavily favored to win.