A roadside bomb has hit a tourist bus near the Pyramids of Giza, south of the capital Cairo, killing three Vietnamese and their Egyptian guide, officials said.
The bus was travelling in the Marioutiyah area near the pyramids on Friday when the crude roadside bomb, concealed by a wall, went off, Egypt's chief prosecutor Nabil Sadeq said in a statement.
The blast wounded 11 other Vietnamese tourists as well as the Egyptian driver.
The bus was carrying a total of 15 Vietnamese tourists, according to Vietnam's Ministry of Foreign Affairs. It said that 10 people were seriously injured.
The tourists were heading to a sound and light show at the pyramids, which they had visited earlier in the day, said Lan Le, 41, who was also on board the bus but remained 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 news agency, speaking at Al Haram Hospital, where the injured were taken.
"I don't remember anything after."
There was no immediate claim of responsibility for the blast.
Prime Minister Mostafa Madbouli visited the injured tourists in hospital, where he announced that the tour guide had died from his wounds.
Madbouli urged against "amplifying" the incident as he insisted that "no country in the world can guarantee that it's 100 percent safe".
"It's possible at times that an individual incident takes place here or there," he told journalists. "We have to know that it's possible that it would be repeated in the future."
Madbouli also told a local television channel that the bus had deviated from a "route secured by the security forces", an assertion also made by the owner of the company that organised the bus tour.
The driver, however, denied the claim to local media.
Vietnamese Ambassador to Egypt Tran Thanh Cong also visited the scene of the attack and Al Haram Hospital, where the victims were being treated.
The bombing is the first deadly attack against foreign tourists in Egypt for over a year and comes as the tourism sector, a vital source of foreign currency revenue, recovers from a sharp drop in visitor numbers since a 2011 uprising that toppled former leader Hosni Mubarak.
Egyptians and tourists have been targeted in recent years as the country's army and police try to suppress armed groups in the Sinai peninsula.
The government says the battle against such groups is a priority as it works to restore stability after the years of turmoil that followed the 2011 protests.
The last deadly attack on foreign tourists in Egypt was in July 2017, when two Germans were stabbed to death in the Red Sea resort of Hurghada.