Israeli police said they heard an explosion from the Egyptian side of the Taba border crossing.

"There is a small smoke cloud near the (border) fence, about 50 meters south of the border crossing," the Ynetnews cited an eye witness as saying.

A pic of the bus blast that took place a while ago in Taba #Sinai#Egypt Wounded are being rushed to hospitals -ONTV pic.twitter.com/lWDbP6AgKs

— Dalia Lachine (@DLachine) February 16, 2014

The Jerusalem Post reported police spokesman Micky Rosenfeld as saying that the incident had been confirmed as a terror attack, which occurred less than a mile from Taba in Sinai.

Egyptian security sources said that an explosive device was set off when the bus passed en route to a hotel in Taba.

The Egyptian Interior Ministry has said that three of those killed were South Korean tourists and the fourth was the bus driver, an Egyptian citizen.

Israeli police and emergency medical services dispatched to the Israel- Taba crossing are on standby to assist if necessary, Rosenfeld said.

No Israelis on tourist bus after explosion took place in Egypt near Taba crossing. Emergency units on standby at Taba crossing Israeli side.

— Micky Rosenfeld (@MickyRosenfeld) February 16, 2014

The small Egyptian town of Taba, a Red Sea resort, is popular among both Israeli and foreign tourists.

The group of 30 tourists was reportedly returning to Taba after an excursion to neighboring Israel. The explosion occurred after the bus, which belonged to Egypt's leading travel agency, Travco, passed through Taba’s checkpoint.

According to Egypt’s Interior Ministry, the bus was traveling from the monastery to nearby Israel when it was attacked.

The AP reported a source as saying that the bus was carrying 33 South Korean tourists visiting the historic St. Catherine's Greek Orthodox monastery in central Sinai.

The attack is the first time tourists have been specifically targeted by militants since army chief Abdel Fattah al-Sisi ousted Egypt’s elected president, Mohamed Mursi of the Muslim Brotherhood, in July 2013. Since then, Al Qaeda-inspired Islamist militants have tended to focus their attacks on security forces in Sinai.

Taba has been the scene of attacks before. One of the deadliest took place in 2004, when 34 people were killed and 160 injured in the Taba Hilton hotel bombing.