An 18-year-old Irishman imprisoned exactly a year ago today for taking part in a protest in Cairo has gone on hunger strike in his cell.

Ibrahim Halawa is facing charges along with hundreds of others in Egypt over protests at Cairo's Al-Fath mosque following the ousting of former president Mohammed Mursi last year.

The judge in Mr Halawa's case walked out of court on Wednesday and refused to continue with the hearing, which means Mr Halawa's period of detention has been extended again.

Speaking to RTÉ News, his sister Somaia said her brother has been on strike since Tuesday's hearing ended without resolution.

She said her brother would only drink water until his release has been secured.

She added that the manner of Tuesday's hearing - in which Mr Halawa was kept in a glass cell and unable to hear or see court proceedings - prompted him to take action.

Ms Halawa said both the Government and, in particular, the European Union could end Mr Halawa's hunger strike immediately by using their powers to guarantee his release.

She said: "Ibrahim will not stop this strike. This is his only; last resort."

She added: "I know loads of people are supporting Ibrahim; but there is only one actual power that we know, the Irish Government, can do a lot. And, we know that the EU can do a lot.

"If a statement comes out from the EU to ask for Ibrahim's immediate release, he will be out tomorrow.

"So, I hope they are not waiting for something to happen to my brother," she added.

Earlier this week, Minister for Foreign Affairs Charlie Flanagan said the Government could not interfere with the judicial process in Egypt.