An explosion ripped through a tourist bus on the Egyptian side of the Taba border crossing with Israel Sunday afternoon, killing four and injuring some 30 passengers.

Three Korean tourists and the Egyptian driver of the bus were killed in the blast, according to Egyptian security officials, while at least eight others sustained serious wounds.

The border crossing, which was sealed in the immediate aftermath of the attack, was later reopened, but only for Israeli citizens seeking to return to Israel.

Officials said the tourist bus had arrived at Taba from the ancient Greek Orthodox monastery of St. Catherine in central Sinai. The bus, filled with 32 Korean Christian pilgrims, had started its journey in Cairo, passed through St. Catherine, and was on its way to Eilat when the bomb exploded shortly before it reached the border.

Egyptian officials said the explosion was caused by a bomb attached to the bus and detonated by either a timer or remote control. The bomb was reportedly placed on the bus at a roadside stop on the drive from St. Catherine to Taba, and detonated as the bus waited near the Taba Hilton hotel to obtain permission to cross into Israel.

Ansar Bayt al-Maqdis, an al-Qaeda affiliated terrorist organization, reportedly claimed responsibility for the attack, various Arabic-language media outlets reported.

The Sinai-based al-Qaeda-linked group was also responsible for a handful of terror attacks throughout Egypt and for several Grad rockets launched at Eilat over the past month from across the border.

Ansar Bayt al-Maqdis is reportedly holed up in the mountainous center of the arid peninsula, an area the Egyptian military has been loath to approach in its ongoing battle with terror groups in the increasingly turbulent Strip.

Egyptian military authorities in the Sinai declared a state of heightened alert and were searching the area along the bus’s route for tracks belonging to the perpetrators of the bombing.

A picture from the scene showed a burnt-out husk of a bus on the side of the road.

No Israelis were among the casualties, an Israeli police spokesman said. Israeli first responders rushed to the border crossing, but an Israel Defense Forces spokesperson said the incident was being managed by Egypt.

Israel halted the operation of the border crossing after the explosion. Israeli officials asked that citizens not try to attempt to reach the border crossing.

The crossing, just a few minutes’ drive from Eilat, is the main civilian crossing point between Israel and Egypt. It is often used by Israeli vacationers, though recent unrest in the Sinai Peninsula has slowed the flow of tourists to a trickle.

In 2004, a bomb blast at a Hilton Hotel in Taba frequented by Israelis killed 31 people. The hotel, which houses a casino, is about 100 meters from the border.