A picture taken on February 16, 2014, shows flames rising from the wreckage of a tourist bus at the site of a bomb explosion in the Egyptian south Sinai resort town of Taba. A bomb tore through a bus carrying South Korean tourists near an Egyptian border crossing with Israel, killing at least four people and wounding 13, officials said. AFP PHOTO / STRSTR/AFP/Getty Images (Str/AFP/Getty Images)

An explosion ripped through a bus carrying South Korean tourists in Egypt’s Sinai Peninsula on Sunday and killed three people, the deadliest attack on vacationers here in years, signaling a potential escalation in the fight by Islamist militants against the Egyptian government.

The insurgency that sprouted last summer had previously confined itself to targeting Egyptian military and police forces. But as the government continues its broad repression of Islamists in the wake of the military’s removal of Islamist President Mohamed Morsi in July, the attacks could turn into a much bloodier ­guerrilla-style conflict, analysts say.

“This is more of a challenge to the government and the state’s authority than there ever was before,” said Kamal Habib, a founding member of Islamic ­Jihad, a group that was at the forefront of a similar revolt in Egypt in the 1990s but that later renounced violence. He noted that today’s insurgents are using heavier weapons, such as missiles and bombs.

The bus blew up Sunday afternoon when it was parked just 200 yards from the Israeli border in the resort town of Taba, sending black plumes of smoke into the sky, according to images on Egyptian state television.

There was no immediate assertion of responsibility for the attack, which killed two South Korean tourists and the Egyptian bus driver, according to the Health Ministry. It had earlier reported that three tourists were killed. At least 15 South Koreans were wounded.

But Habib said the blast indicates that militants have adapted their strategy to try to cripple the government by hitting the country’s vital and ailing tourism industry. The military-appointed cabinet has pinned its legitimacy on a return to stability and economic revival after three years of turmoil that began with the Arab Spring uprising.

“This is likely the beginning of a new phase” of the conflict between militant Islamists and the state, Habib said.

Government crackdown

The insurgency has steadily expanded since August, when Egyptian security forces launched a crackdown on Morsi’s supporters, killing more than 1,000 civilians, according to human rights groups. Since then, the government has arrested thousands of people associated with Morsi’s Muslim Brotherhood or other opposition groups and passed laws strictly limiting protests.

For their part, the militants have killed at least 100 police officers and soldiers since August, more than 30 of them this year. Groups such as the Sinai-based Ansar Bayt al-Maqdis, the most powerful of the emerging militant organizations, have repeatedly urged Egyptians to stay away from security installations, which they say are legitimate targets.

The government has responded to the insurgency with increased raids in the northern part of Sinai, where many Islamist militants are based.

In addition, after a deadly car bombing at a security building in the Nile Delta in December, which was claimed by Ansar Bayt al-Maqdis, authorities declared the Brotherhood a “terrorist organization.” The two groups have no known connection, and the Brotherhood renounced violence decades ago.

Authorities in recent weeks have frozen the assets of Islamist-run charities, jailed journalists with suspected Brotherhood sympathies and charged peaceful activists from the moderate Islamist Strong Egypt Party with terrorism.

Analysts say the persecution of Islamists who had tried to advance their agenda through the political system has driven people to join extremist groups — which now have between 500 and 2,000 fighters, based on various estimates.

“If you blame every Islamist in society, you will make an enemy out of all of them,” said Safwat el-Zayat, a former brigadier general in the Egyptian army. “This is going to be a long war.”

The message from Ansar Bayt al-Maqdis to political Islamists “from the beginning was that the ballot box is not legitimate; it is arms that will guarantee your survival,” said Omar Ashour, a specialist in Islamist movements at the Brookings Doha Center.

Hard-liners had blasted the Brotherhood and other Islamist political parties for participating in the elections that followed the toppling of strongman Hosni Mubarak in 2011. After the military overthrew Morsi, Egypt’s first democratically elected president, the message from the militant Islamists “was heard loud and clear,” Ashour said.

Motive in bus blast unclear

In recent weeks, violence between the insurgents and the military has intensified. On Jan. 24, Ansar Bayt al-Maqdis detonated a large car bomb outside a security headquarters in Cairo, the first of four blasts that would kill six people in the capital that day.

Less than 24 hours later, the group’s fighters for the first time shot down a military helicopter with a heat-seeking, shoulder-fired missile, killing five soldiers. In response, the army leadership announced an expanded military offensive in North Sinai, where the group is based.

The move against Ansar Bayt al-Maqdis, which residents in North Sinai said forced some fighters to flee to the nearby Gaza Strip, could have pressured insurgents to lash out and attack foreign tourists, Habib said. But the motive for going after tourists remains unclear.

Ansar Bayt al-Maqdis has shown increasing sophistication and prowess, but analysts say there is little indication that it has recruited a substantial number of trained foreign fighters or established logistical ties with al-

Qaeda or its affiliates. The majority of its fighters are Bedouin tribesmen from Sinai’s Sawarka tribe or Egyptians from the Nile Delta, according to military analysts and Sinai residents with knowledge of the group’s composition.

None of the other, smaller cells that have emerged on the Egyptian militant scene in the past few months — including Ajnad Misr, which means “Soldiers of Egypt” — have demonstrated ambitions beyond targeting local police or Egyptian soldiers.

Ruth Eglash in Jerusalem and Sharaf al-Hourani in Cairo contributed to this report.