At least four people were killed and about a dozen others were injured Friday when a roadside bomb detonated near a tour bus close to the pyramids of Giza in Egypt.
Three Vietnamese tourists and the bus driver, who was Egyptian, were killed in the blast. Eleven others were injured, according to The Guardian.
A bomb hidden beside a wall on Cairo's outskirts went off as the bus, which was carrying 14 Vietnamese tourists, passed it, the outlet reported.
Police and medical personnel arrived on the scene, transporting those injured in the attack to hospitals. According to The Guardian, Egyptian Prime Minister Mostafa Madbouly visited those taken to Al-Haram hospital.
Madbouly told reporters that the bus had taken an alternate route, traveling along a road that was not secured by the police.
ABC News reported that the attack occurred about 6 p.m. local time. Egypt's Interior Ministry has not yet released information about any suspects in the bombing. No individual or group has claimed responsibility for the attack.
Vietnam Foreign Minister and Deputy Prime Minister, Pham Binh Minh, said he was "deeply saddened" by Friday's attack.
"MoFA Vietnam (Vietnam's Ministry of Foreign Affairs) stays beside victims of the #TourBusAttack & their families, in close coordination with Egyptian Govt on the case," he tweeted.
Ahmed Hafez, a spokesperson for the Egyptian Foreign Ministry, called the bombing an act of terrorism.
"The bombing of the tourist bus in El-Maryoutiya, a despicable, cowardly terrorist act which targets what cannot be targeted: The determination of Egypt and the Egyptians," he wrote on Twitter.
"We extend our sincere condolences to the victims' families in Vietnam and Egypt. We will continue to move towards a new year of determination to root out terrorism," he added.
In a statement, State Department spokesman Robert Palladino condemned the attack, expressing condolences to the families of the victims.
"The United States strongly condemns the attack carried out today on a tourist bus in Giza. Our deepest condolences go out to the families of those killed and we wish a quick recovery for those injured," Palladino said.
According to Palladino, the State Department has not been made aware of any American casualties.
"We stand with all Egyptians in the fight against terrorism and support the Egyptian government in bringing the perpetrators of this attack to justice," he added.
Friday's attack comes as Egypt continues to focus on efforts to boost tourism following years of political unrest and attacks on tourists.
Last year, two German tourists were killed and four others were injured at a popular resort on the Red Sea in Hurghada, Egypt.
Tourism has been a key contributor to the country's economy, making up about 11 percent of the company's gross domestic product last year, according to the World Travel and Tourism Council.
— This report was last updated Dec. 29 7:10 a.m.