British Prime Minister Theresa May telephoned Egyptian President Abdel-Fattah El-Sisi on Saturday to express her condolences over the "barbaric attack" on a mosque in North Sinai on Friday, saying the UK "stands ready to help in any way possible."
The gun-and-bomb attack by Islamist militants killed more than 300 people and left tens injured during Friday prayers.
"The prime pinister offered her personal condolences and the condolences of the British people for the barbaric attack that took place at Al-Rawdah mosque in North Sinai," a Downing Street spokesperson said on the UK government's website.
He said the two leaders "spoke about the attack being a terrible example of the threat Egypt faces."
The British PM told El-Sisi that the UK "stands ready to help in any way possible," he added.
Around 30 terrorists flying the black flag of the Daesh terrorist group encircled the mosque and massacred worshippers during Friday prayers, leaving 305 people dead, including 27 children, and 128 injured.
Egypt's military responded with airstrikes against militant hideouts in North Sinai.
Friday's attack was Egypt's deadliest in recent history, prompting a flurry of international condemnation, including from the UN, US President Donald Trump and the Vatican's Pope.
On Saturday, Algerian President Abdelaziz Bouteflika sent a message of condolence to El-Sisi, condemning the "heinous crime".
According to Egypt's state-run news agency MENA, Bouteflika reaffirmed Algeria's "absolute solidarity with the brotherly Egyptian people" and renewed support for Egypt it in the face of terrorism.