Police told the AFP news agency the three judges were travelling on a bus in the city of al-Arish, Sinai, when it was attacked by gunmen.

Several other people were also said to be injured.A militant believed to support Mohamed Morsi during attacks on security forces in al-Arish after he was deposed in August 2013

It is unclear whether the attack was linked to anger over the death sentence passed for Mr Morsi in Cairo.

His Muslim Brotherhood party has been banned and hundreds of its former officials and supporters have been arrested and jailed.

The Sinai Peninsula has seen frequent outbreaks of violence in recent months and terrorist attacks prompted the Egyptian government to declare a state of emergency last year.

In January, an Isis-affiliated group claimed responsibility forrocket and bomb attacks on the military and police that killed at least 26 people.

Al-Arish is just 30 miles from the Rafah crossing between Egypt and the southern Gaza Strip

The Foreign and Commonwealth Office (FCO) has raised concern about the deteriorating situation and advises against all travel to North Sinai, where al-Arish is situated.

“Terrorists and criminals seek to prevent the Egyptian authorities from exercising control,” a spokesperson said.

“There are regular bomb attacks against government buildings, security forces and energy infrastructure.

“The al-Arish area has seen many attacks, but the whole of the North Sinai region is at risk.”

The Egyptian army are fighting militants in the area and several hundred people are believed to have died in battles since July 2013, when security forces were attacked by people angry at the coup against Mr Morsi.

Sinai borders the Gaza strip and Egyptian state prosecutors have claimed that Mr Morsi colluded with the Palestinian Hamas group while his predecessor was being overthrown during the Arab Spring.

They alleged that during the 18-day uprising in 2011, militants passed through illegal tunnels between Gaza and Sinai to enter Egypt and help hundreds of Muslim Brotherhood supporters, including Mr Morsi, escape jails in the capital in violent prison breaks.

Mr Morsi has also faced charges relating to the killing and torture of protesters, passing state secrets to Hamas, Hezbollah and Qatar, fraud and “insulting the judiciary”. He has rejected the courts’ authority and his supporters say all the cases are politically motivated.