Britain's Foreign Secretary William Hague said on Monday it was summoning Egypt's ambassador over the prison sentences handed down to journalists working for Al-Jazeera.
"I have instructed officials to summon the Egyptian Ambassador to the Foreign and Commonwealth Office today," Hague said in a statement.
A spokesman for Prime Minister David Cameron said he was "completely appalled" by the verdicts.
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The comments came after an Egyptian court sentenced three Al-Jazeera journalists including Australian Peter Greste to jail terms ranging from seven to 10 years, accusing them of aiding the blacklisted Muslim Brotherhood.
Two British journalists working for the network, Sue Turton and Dominic Kane, were among 11 defendants being tried in absentia out of 20 overall. They were handed 10-year sentences.
Greste and Egyptian-Canadian Mohamed Fadel Fahmy each got seven years, while producer Baher Mohamed received two sentences -- one for seven years and another for three years.