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CAIRO, Feb 18 (Reuters) - The Islamist militant group Ansar Bayt al-Maqdis said on Tuesday the bombing of a tourist bus in Egypt's Sinai that killed two South Koreans and the Egyptian driver on Sunday was a suicide attack carried out by one of its fighters, and threatened more strikes against economic targets.
The attack on the bus, which was travelling to Israel from St. Catherine's Monastery, a popular tourist destination in the south Sinai, was the first assault on tourists since President Mohamed Mursi's ouster spurred an Islamist insurgency.
"Ansar Bayt al-Maqdis has successfully sacrificed one of its heroes to detonate the bus headed toward the Zionists, and this comes as part of our economic war against this regime of traitors," the group said in a statement.
Islamist militancy has risen sharply in Egypt, including the largely lawless region adjoining Israel and the Gaza Strip, since the army deposed Islamist Mursi in July, following mass protests against his rule.
Since then the army has launched a wide-scale operation in Sinai targeting Islamist militants, and security forces launched a crackdown on Islamists and Mursi's Muslim Brotherhood which authorities labelled a terrorist organisation. The Brotherhood denies any links to violence.
"With God's will we will be watching this treacherous gang of inflitrators and we will target their economic interests in all places in order to paralyse their hands from (hurting) Muslims," the Ansar Bayt al-Maqdis statement said.
The attack marks a shift in strategy among Sinai's militants to targeting "softer" tourist and economic targets. Egypt's vital tourism industry has already been hit hard by three years of political turmoil and street protests.
Islamist militants launch near-daily attacks on security forces in northern Sinai, while the south, with its many Red Sea resorts, had been seen as a relatively safe tourist destination.
Ansar Bayt al-Maqdis has claimed responsibility for several bombings, including an attempt to kill the interior minister in Cairo last year. The organization also said it was behind a missile attack on a military helicopter last month that killed five soldiers.
The bus attack revived memories of an Islamist uprising in the 1990s that often targeted tourists and took years for then-President Hosni Mubarak to crush.
In 2004, a bombing at the Sinai resort of Taba killed 34 people, including Israeli tourists.
Army chief Field Marshal Abdel Fattah al-Sisi, who was behind Mursi's ouster, is expected to announce his candidacy for the presidency soon.
Sisi had hoped a political roadmap unveiled after Mursi's overthrow would stabilize Egypt, which has a peace treaty with Israel and controls the Suez Canal, a busy world shipping channel on the Sinai's western edge. (Reporting by Asma Alsharif and Ali Abdelatty; Editing by Mohammad Zargham)