William Hague “emphasised UK condemnation of all acts of violence” and urged dialogue, it said.
Earlier, state media said security forces cleared a Cairo mosque after a day-long stand-off with Muslim Brotherhood supporters.
Mr Hague stressed “attacks on mosques and churches were unacceptable”.
Egypt’s security forces said all the protesters had now been taken out of the al-Fath mosque.
It followed a day which saw exchanges of gunfire between security forces and protesters.
A UK Foreign Office spokesperson said Mr Hague and Egyptian Foreign Minister Nabil Fahmy had spoken “about the tragic violence and loss of life over recent days”.
“The foreign secretary emphasised UK condemnation of all acts of violence, whether disproportionate use of force by the security forces or violent actions by some demonstrators,” they said.
“The foreign secretary noted the Egyptian government’s stated commitment to the political roadmap published on 4 July, based on dialogue between all parties who accepted peaceful political processes,” the spokesperson added.
“He underlined the need for urgent steps by all sides to end the violence and enable a return to dialogue.”
The spokesperson said Mr Hague had also emphasised the European Union’s “collective determination to support a peaceful resolution of the situation”.
In London on Saturday, supporters of ousted President Mohammed Morsi demonstrated outside the Egyptian embassy for a second day.
About 200 people gathered outside the building in Knightsbridge.
Nearby, about 50 cars emblazoned with slogans including “stop the murder” and “pro-democracy” took part in a procession, with occupants of the vehicles waving Egyptian flags and giving peace signs.
The UK Foreign Office had said on Friday that it was “deeply concerned” about the ongoing violence in Egypt.
It is advising against all travel to north Sinai and all but essential travel to the rest of Egypt, with the exception of Red Sea resorts.
A crackdown on protest camps in Cairo on Wednesday left hundreds of people dead. Further clashes on Friday killed at least another 173 people.
A state of emergency is in force, including a dusk-to-dawn curfew.
Meanwhile, Egypt’s interim Prime Minister Hazem Beblawi has proposed legally dissolving the Muslim Brotherhood.
The group supports Mr Morsi, and wants him to be reinstated.