CAIRO - Egyptian Prime Minister Mostafa Madbouly Friday ordered the highest healthcare and treatment for those injured in a bus blast that left three Vietnamese tourists and their Egyptian tour guide dead.

A total of three Vietnamese tourists and an Egyptian tour guide were killed Friday when a home-made bomb hit a bus carrying foreign tourists in Marioutiya area near the Giza Pyramids.

At least 10 tourists and the Egyptian driver were also injured in the attack.

"The state will deal with iron fist with those who plot to harm the country's security and the safety of its people and visitors," Madbouly told reporters during his visit to the injured in a Cairo hospital.

Madbouly urged the international community to unite in the face of terrorism, noting that such incidents cannot stop the Egyptians' development.

The Egyptian prime minister revealed that the attack happened "because the route of the bus was changed," pointing out all tourist buses are always accompanied by police patrols.

Madbouly did not tell who or how the route of the bus was changed, but said an investigation to uncover the details of the incident has already been launched.

According to the Egyptian Interior Ministry, security forces moved to the scene and started an investigation into the attack.

Right after the attack, Egypt's general prosecutor also ordered an urgent investigation into the incident.

Egyptian state media reported that a team of the general prosecution and the supreme state security prosecution inspected the scene of a blast and collected samples from the site for more investigation to identify the perpetrators.

Meanwhile, the deadly attack was widely criticized by the Egyptian official and foreign countries.

Head of the European Union (EU) Delegation to Egypt Ivan Surkos strongly deplored the attack.

"The EU stands hand in hand with Egypt in the fight against terrorism," the EU envoy said in a statement. "Our condolences to families of the victims. Speed recovery to the injured."

The Kuwaiti Emir Sheikh Sabah Al-Ahmad Al-Jaber Al-Sabah sent a cable to Egyptian President Abdel-Fattah al-Sisi, expressing Kuwait's condemnation of the explosion, Egypt's official MENA news agency reported.

He stressed Kuwait's support for Egypt and all the measures to protect its security and stability.

The Bahraini Ministry of Foreign Affairs has also condemned the terror attack, affirming the kingdom's full solidarity with Egypt in its efforts to combat violence and terrorism of all forms, and vowed support to its efforts to enhance security and peace.

The attack came days before Egyptians celebrate New Year and Christmas, which is marked by Coptic Egyptians on Jan. 7.

Copts make up 10 percent of Egypt's 100 million population.

This week, Egypt's armed forces, in coordination with the Ministry of Interior, intensified measures to secure Christmas and New Year's celebrations nationwide.

The army and police said they have deployed forces to ensure the safety of citizens at places of worship and vital facilities, adding that all forces have been trained on how to deal with threats that may disturb the celebrations.

Egypt has been fighting against a wave of terror activities that killed hundreds of policemen and soldiers since the military toppled former Islamist President Mohamed Morsi in July 2013 in response to mass protests against his one-year rule and his currently blacklisted Muslim Brotherhood group.

Terror attacks in Egypt had mainly targeted police and military men in North Sinai before spreading nationwide and targeting the Coptic Christian minority as well, leaving dozens of them dead.

Terrorists attacked two Coptic churches in the cities of Tanta and Alexandria in early April last year, killing a total of 47 people and wounding 106 others.

Most of the attacks were claimed by a Sinai-based group loyal to the Islamic State extremist group.