At least four people have been killed and another 10 injured after a roadside bomb exploded near a bus carrying Vietnamese tourists close to the pyramids in Giza.

Three of the dead were Vietnamese and one was an Egyptian tour guide.

An Egyptian security source told the Guardian the bus had 16 people onboard and an IED exploded as it approached. Reuters reported that the device was hidden near a wall on Marioutiya Street on the Cairo outskirts.

Police and ambulances attended the scene, and the injured were transferred to nearby hospitals.

The tourists were heading to a show at the pyramids, which they had visited earlier in the day, said Lan Le, 41, who was onboard the bus but unhurt.

“We were going to the sound and light show and then suddenly we heard a bomb. It was terrible, people screaming,” she told Reuters, speaking at Al-Haram hospital. “I don’t remember anything after.”

Ahmed Samy, a tuk-tuk driver, said he saw the bus after the blast and locals and drivers were helping the injured to get out. “One of the passengers was dead and was covered in blood,” he said.

The Egyptian prime minister, Mostafa Madbouly, visited the injured at Al-Haram hospital. He told reporters that the bus had not followed the path it was supposed to take, where it would have been secured by the police.

Reuters said that the Egyptian driver of the bus later told local media he had not deviated from the route.

Egyptian prosecutors said they had launched an urgent investigation “to arrest the perpetrators”.

Tourism has been one of the main drivers of Egypt’s struggling economy, contributing around 375bn Egyptian pounds (£16bn), or 11% of GDP, in 2017, according to the World Travel and Tourism Council.

The country has intensified efforts to woo tourists after a sharp decline in numbers following the political turmoil linked to the 2011 revolution. Tourism to Egypt’s Red Sea resorts, which had been spared the worst of the political upheaval, also fell dramatically following an explosion onboard a Russian plane over the Sinai peninsula on 31 October from Sharm el-Sheikh international airport. The explosion claimed the lives of all 217 passengers and seven crew members.

Targeted campaigns promoting tourism have been going hand in hand with huge state-sponsored international conferences designed to promote youth empowerment, technology and foreign investment.

No militant group has yet claimed responsibility for Friday’s attack. The most active group has been Islamic State, which has been operating mainly in North Sinai. An Isis-linked group claimed responsibility for the explosion on the Russian plane.

Isis also claimed responsibility for a January 2016 attack in Hurghada where two militants entered a hotel and stabbed three tourists. The Swede and two Austrians survived.

In February 2014, the militant group Ansar Bayt al-Maqdis, which later pledged allegiance to Isis, claimed a bomb attack that ripped through a tourist bus on the Egyptian side of the Taba border crossing with Israel, killing four and injuring about 30 passengers.

Before the Russian plane explosion, the deadliest attack to target tourists took place in Luxor in 1997 when more than 60 people, the vast majority foreign visitors, were murdered by militants armed with guns and knives.