At least 18 people were killed and 40 were wounded by a blast in front of a Christian church in Alexandria, Egypt on Palm Sunday, according to local reports, hours after at least 30 people were killed by a blast in the Nile Delta city of Tanta.

Islamic State claimed responsibility for both attacks, via its Amaq press agency. "A group that belongs to Islamic State carried out the two attacks on the churches in the cities of Tanta and Alexandria," Amaq said.

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ISIS also threatened that there would be more attacks against Egyptian Christians, saying in an online statement carried by Amaq, "Let the crusaders and apostates know that they will pay a huge bill with their son's blood."

Open gallery view A map showing Tanta and Alexandria in Egypt.

The Alexandria attack, which hit the historic seat of the Coptic Pope, was carried out by a suicide bomber, Egypt's Health Ministry said, adding that three police officers were killed in the attack.

The Coptic Pope Tawadros II had been leading the ceremony, but reportedly left the church before the blast occurred.

Open gallery view A relative of one of the victims reacts after a church explosion killed at least 21 in Tanta, Egypt, April 9, 2017. REUTERS/Mohamed Abd El Ghany Credit: MOHAMED ABD EL GHANY/REUTERS

Tawadros said afterward, "These sinful acts will not undermine the unity of Egyptians against terrorism."

U.S. President Donald Trump tweeted: "So sad to hear of the terrorist attack in Egypt. U.S. strongly condemns. I have great confidence that President Al Sisi will handle situation properly."

Egyptian President Abdel Fattah al-Sissi said in a statement he had ordered the immediate deployment of soldiers to assist police in protecting "vital facilities" across the country.

He condemned the attacks and summoned the National Defense Council to an urgent session. According to local reports, he also announced three days of national mourning.

"The attack ... will only harden the determination (of the Egyptian people) to move forward on their trajectory to realize security, stability and comprehensive development," Sissi said.

Prime Minister Benjamin Netanyahu's office released a statement in wake of the attacks, saying that, “Israel sends condolences to the families of those murdered in the attack in Egypt and wishes for recovery for the injured. The world must unite and fight terrorism everywhere.”

Israel also restated its warnings telling Israelis in Sinai to return home immediately, citing the threat of terrorism.

The U.S. embassy in Cairo tweeted in response to the attacks, saying "We condemn this hateful act targeting worshippers as they celebrated one of the most sacred days in Christianity. We grieve with all Egyptians as we express our most heartfelt condolences to the victims and their families and we hope for a speedy recovery for those injured in the attack."

An unconfirmed video surfaced on social media claiming to show CCTV footage of one of the bombings.

Turkish presidential spokesman Ibrahim Kalin tweeted his condolences and said, "We strongly condemn the heinous terror attacks on churches in Egypt on Palm Sunday today."

The attacks were the latest in a series of assaults on Egypt's Christian minority, which makes up around 10 percent of the population of 92 million and has been repeatedly targeted by Islamic extremists. It comes just weeks before Pope Francis is due to visit Egypt.

Open gallery view People looking at the aftermath following a bomb blast which struck worshipers gathering to celebrate Palm Sunday at the Mar Girgis Coptic Church in the Nile Delta City of Tanta on April 9, 2017. Credit: STRINGER/AFP

Following the attacks, the pontiff expressed his "deep condolences" to the Coptic patriarch, Tawadros II, calling him "my brother," to the Coptic church and "all of the dear Egyptian nation," and said he was praying for the dead and injured in the attack that occurred just hours earlier as Francis himself was marking Palm Sunday in St. Peter's Square.

The pontiff asked God "to convert the hearts of those who spread terror, violence and death, and also the hearts of those who make, and traffic in, weapons."

The pope's remarks on the church attack were handed to him on a piece of paper after he remembered the victims of the Stockholm attack Friday night.

CBC showed footage from inside the church in Tanta, where a large number of people gathered around what appeared to be lifeless, bloody bodies covered with papers.

Open gallery view The Pope of the Coptic Orthodox Church. Credit: Amr Nabil/AP

"There was a huge explosion in the hall. Fire and smoke filled the room and the injuries were extremely severe. I saw the intestines of those injured and legs severed entirely from their bodies," Vivian Fareeg told Reuters by phone.

A militant group called Liwa al-Thawra claimed responsibility for an April 1 bomb attack targeting a police training center in Tanta, which wounded 16 people. The group, believed to be linked to the outlawed Muslim Brotherhood, has mainly targeted security forces and distanced itself from attacks on Christians.

In December, 25 were killed by a suicide bombing at Cairo's main Coptic cathedral. ISIS later claimed responsibility for the blast.

Egypt has seen a spate of attacks since 2013, when the army deposed Egypt's former Islamist President Mohammad Morsi, the country's first democratically elected leader, following mass protests against his divisive rule.

Christians backed Morsi's toppling by then-army chief al-Sissi, Egypt's current president.

The Associated Press contributed to this report.