CAIRO, Feb 13 (Reuters) - Egyptian politician Hamdeen Sabahi on Wednesday called for the release of what he termed "prisoners of conscience," days after he announced he would run for president.

Egypt is preparing for presidential and parliamentary polls due within six months under a political transition plan set out after the army ousted President Mohamed Mursi in July following mass protests against his rule.

Since Mursi was deposed, hundreds of his Islamist supporters have been killed and thousands arrested in a crackdown on the Muslim Brotherhood. Some well-known secular dissidents have also been jailed in recent months for protesting without permission.

"At the moment there are real prisoners of conscience in Egypt," Sabahi said in an interview with a privately-owned television channel. He was referring to young people involved in the 2011 uprising that swept autocrat Hosni Mubarak from power and the 2013 protest movement against Mursi.

"I demand that those leave in freedom in the style appropriate for a country under the rule of law," he said.

Sabahi, 59, came in third in 2012's presidential elections, won by Mursi. At the time, the leftist candidate built a large following, using a popular touch among voters to top candidates with better-funded campaigns.

Field Marshal Abdel Fattah al-Sisi, the army chief who ousted Mursi, has yet to announce his candidacy, but is widely expected to win the presidency easily. The interim government has declared the Brotherhood a terrorist organisation.

Secular activists arrested last month on the third anniversary of the revolt against Mubarak have told relatives and lawyers that they have been tortured, some with electric shocks. The Interior Ministry has denied any abuses.

"I don't accept either the existence of a prisoner because he has an opinion while not having any connection with terrorism, or the existence of any kind of torture," Sabahi said.

"The children of the revolution are imprisoned and the corrupt of the Mubarak regime have reappeared and these two things create feelings of fear."

Also on Wednesday, the public prosecutor sent 143 people to trial on charges of involvement in an August attack on a police station in Kerdasa, near Cairo, in which at least 11 policemen were killed.

The building was hit with rocket-propelled grenades and burned down after police had stormed Islamist protest camps in Cairo the same day and killed hundreds of Mursi supporters.

The government has said it is fighting terrorism. Deadly attacks on security forces have intensified since last July with shootings and bombings spreading beyond the Sinai Peninsula into the Nile Delta and the capital.

Egyptian state television reported late on Wednesday a police sergeant was killed in a shooting at a church in Cairo's Ain Shams district. (Reporting by Omar Fahmy, Ali Abdelaty and Shadia Nasralla, writing by Shadia Nasralla; editing by Alistair Lyon and G Crosse)