The Islamist militant group Ansar Bayt al-Maqdis said on Tuesday the bombing of a tourist bus in Egypt's Sinai that killed three 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 Morsi'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."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.“Egypt’s tourism industry has been suffering for the past couple years as a result of the persistent political instability and steady stream of reported violence. Over the past few months, however, Cairo has been engaged in a serious effort to draw tourists back and there were some signs of minor improvement. This weekend’s attack in Taba will likely set these efforts back,” David Barnett, research associate at the Foundation for Defense of Democracies and a contributor to the Long War Journal website, told The Jerusalem Post.“Whether tourists in Egypt are regularly targeted now by Ansar Bayt al-Maqdis remains to be seen,” said Barnett, who closely follows events in Sinai.Reports surfaced that the group also warned tourists on Tuesday to leave Egypt and threatened to attack any who stay after February 20, citing a statement made by a Twitter account thought to be linked with the organization.However, Barnett says that Maqdis has no official Twitter account and that the group’s claim of responsibility for the bus attack came in an official statement. “It is a fraud,” said Barnett, pointing out that the account has claimed attacks that the group never claimed responsibility for. “Jihadists do not promote the account, but rather urge each other to report it for spam so that Twitter shuts it down.” State television quoted Prime Minister Hazem el-Beblawi as saying Ansar was a threat to tourists. It aimed, he said, to derail the roadmap to elections unveiled by the army when Morsi's fall provoked the bloodiest internal crisis in Egypt's modern history.In another sign of instability, an explosion wounded four Egyptian soldiers in the Sinai on Tuesday, state-run Al Ahram newspaper reported on its website.Tourism was a major employer and accounted for more than 10 percent of gross domestic product before the revolt.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.