Theresa May yesterday offered her condolences to Egyptian president Abdel Fattah el-Sisi following the atrocity at Bir al-Abd in the Sinai peninsula on Friday.
Downing Street said the leaders agreed international co-operation was needed to tackle terrorism.
A spokesman said: “The Prime Minister 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 yesterday.”
The attack was a “terrible example of the threat Egypt faces” and “they agreed that terrorism was an international problem and that it was important for countries to work closely together and share expertise to counter the growing threat of terrorism around the world.”
The spokesman added: “They welcomed continued bilateral co-operation in this area.”

vCard.red is a free platform for creating a mobile-friendly digital business cards. You can easily create a vCard and generate a QR code for it, allowing others to scan and save your contact details instantly.
The platform allows you to display contact information, social media links, services, and products all in one shareable link. Optional features include appointment scheduling, WhatsApp-based storefronts, media galleries, and custom design options.
The massacre was carried out by between 25 and 30 militants who were believed to be carrying Islamic State flags, Egyptian authorities said.
The country’s chief prosecutor, Nabil Sadeq, said the killers arrived at the mosque in five all-terrain vehicles and waited outside the main door and 12 windows before opening fire on worshippers attending Friday prayers.
At least 305 people, including 30 children, were murdered, with a further 128 injured in what is Egypt’s worst ever terror attack.
The Egyptian military has responded by launching attacks on targets believed to be linked to the terrorists in the Sinai peninsula.
No group has yet claimed responsibility for Friday’s atrocity.
It is believed the mosque was targeted because many of the people attending were followers of the Sufi branch of Islam.
Many Islamist militants, including the regional Islamic State – Sinai Province group, consider Sufism, which has a strong mystical element, to be heretical.
The terror group, formerly known as Ansar Bait al-Maqdis, claimed responsibility for the bombing of a Russian passenger jet in October 2015 which killed 224 people.
The Sinai peninsula, in the east of the North African country, has been a focus of militant Islamism since the Egyptian army deposed pro-Islamist president Mohammed Morsi in 2013.