Governments around the world have condemned the beheadings of 21 Egyptian Christians in Libya by Islamic State (IS) militants.
White House spokesman Josh Earnest described the beheadings as a "despicable and cowardly murder" and called for a political settlement in war-torn Libya.
"This wanton killing of innocents is just the most recent of the many vicious acts perpetrated by ISIL-affiliated terrorists against the people of the region, including the murders of dozens of Egyptian soldiers in the Sinai, which only further galvanizes the international community to unite against ISIL," Earnest was quoted as saying.
The UK Prime Minister David Cameron said, in a tweet, the murder of 21 Egyptian Coptic Christians is a “cruel and barbaric act.” He reiterated the UK “will not waver in our fight against terrorists and extremism.”
France's President Francois Hollande said the killing was "savage." According to Reuters, Hollande's office said he "expresses his concern about the extension of Daesh [IS] operations in Libya and reminds of the determination of France and its allies to fight against this group."
Hollande and El-Sisi had a phone conversation during which they emphasised "the importance that the Security Council meet and that the international community take new measures" against the spread of IS in Libya," AFP reported.
The UN Security Council condemned the killing of Egyptian Coptic Christians and offered condolences to the families of the victims and Egypt's government and people, Egypt's state-run news agency MENA reported.
The Security Council, in its statement, stressed the necessity of fighting "terrorist crimes" that signify a threat to international peace and security in accordance with the UN Charter.
Also according to MENA, Egypt’s UN Ambassador Amr Abu Al-Atta said he started immediately contacting member states of the Security Council to issue a "tough, condemnatory statement" once IS revealed the beheading video.
Bahraini King Hamad Bin Isa Al-Khalifa sent a telegram of condolence to El-Sisi to accentuate his "severe condemnation of this criminal act by the IS," Bahrain News Agency reported.
King Hamad said Manama "will back any measures Egypt sees as suitable to encounter such a terrorist organisation" and support the international community in its endeavors to eradicate IS and cut its roots."
UAE Foreign Minister Sheikh Abdullah bin Zayed Al-Nahyan said IS committed an "ugly crime," Emirates News Agency (WAM) reported.
"The United Arab Emirates is devoting all its resources to support the efforts of Egypt to eradicate terrorism and the violence directed against its citizens and reaffirms its total support for Egypt," WAM quoted him as saying in a statement.
The UAE's top diplomat added that such an ugly crime "underlines the necessity for the Arab and international community to stand by the legitimate Government and the Libyan people, under the leadership of the elected Libyan Parliament and the Government it has formed."
Last August, both Egypt and the UAE denied media reports that their militaries bombed militant-controlled areas in the Libyan capital city of Tripoli.
Arab League chief Nabil El-Arabi called for the activation of the Treaty of Joint Defense and Economic Cooperation to "preserve the Arab national security and encounter the terrorism phenomenon."
According to Kuwait News Agency (KUNA), El-Arabi offered his condolences to El-Sisi, Pope Tawadros, families of the beheaded Egyptian Copts and the Egyptian society.
Kuwaiti Emir Sheikh Sabah Al-Ahmad Al-Jaber Al-Sabah offered condolences to El-Sisi, emphasizing his country's backing to counterterrorism efforts of the international community, MENA reported.
Sudan's Foreign Ministry spokesman Youssef El- Kordofani offered condolences to Egypt and the families of the beheaded Egyptians, stating Khartoum's "solidarity" with Cairo, reported MENA.
El-Kordofani said the killing is a "heinous and brutal crime that contradicts the rules and teachings of the Islamic religion."
Palestinian President Mahmoud Abbas offered his condolences to El-Sisi and the head of Egypt's Coptic Orthodox Church, Pope Tawadros II. Abbas declared national mourning for three days, the Palestinian News and Info Agency (WAFA) said.
"At such tough moments, we can do nothing but support and be in solidarity with President El-Sisi and the Egyptians," WAFA quoted Abbas.
On Sunday night, El-Sisi commissioned Egypt's Foreign Minister Sameh Shoukri to travel to New York in order to hold talks with senior United Nations officials and members of the Security Council.
The minister, El-Sisi said, would "demand the international community live up to its responsibilities by taking necessary actions in line with the UN convention, and to declare that what is happening in Libya threatens international peace and security."
On Monday morning, the Egyptian army launched airstrikes on Monday morning against IS targets in Libya, including training camps and army depots.
President Abdel-Fattah El-Sisi had said on Sunday night that Egypt reserves the right to retaliate against the killing of its citizens as he addressed the nation in a televised speech.
Also on Sunday night, Libya's strongman General Khalifa Haftar, who is currently leading operations against Islamist militants in Libya, said he "strongly backs an Egyptian military intervention" in Libya in a phone interview with Egypt's Dream TV anchor Wael El-Ebrashy."
Borders should not hinder any retaliatory strikes against these terrorist groups, and we do not reject any means of weakening such groups," Haftar said.