* Press freedom group says 18 journalists in jail
* Most accused of links to the Muslim Brotherhood
* Reporters unable to enter Sinai where army fights insurgency
By Ahmed Aboulenein
CAIRO, June 25 (Reuters) - Egypt is holding the highest number of journalists behind bars since record keeping began, using the pretext of national security to crack down on press freedoms, the Committee to Protect Journalists said on Thursday.
A prison census conducted by the CPJ on June 1 found at least 18 Egyptian journalists were being held in jail for reasons related to their reporting, the most in Egypt since the CPJ began recording data on imprisoned journalists in 1990.
"The threat of imprisonment in Egypt is part of an atmosphere in which authorities pressure media outlets to censor critical voices and issue gag orders on sensitive topics," the CPJ said in a report published on Thursday.
Khaled al-Balshy, the head of the freedoms committee of Egypt's press syndicate, said the number of journalists imprisoned was higher, putting it at more than 30.
"We are in the worst climate for journalism in Egypt's history," he told Reuters.
Reuters could not independently confirm the number in detention in Egypt.
CPJ said most of the journalists imprisoned are accused by the government of belonging to or being affiliated with the Muslim Brotherhood, which Cairo designates as a terrorist group.
Authorities say the Brotherhood is a threat to national security and they deny allegations of abuses. Some of the journalists denied charges of links to the Brotherhood.
"These numbers are not accurate and this report is not objective," a government source told Reuters, adding that all imprisoned journalists were facing criminal charges and were not imprisoned for political or free speech reasons.
Six journalists were sentenced to life in prison and several others are being held in pretrial detention without a set date for a court hearing, the CPJ reported.
"The arrests of journalists in Egypt are often violent and involve beatings, abuse, and raids of their homes and confiscation of their property," the CPJ said.
"Their prison cells are often unclean and overcrowded. In letters from prison, some journalists wrote that they often do not see sunlight for weeks; others described the torture of prisoners, including the use of electric shocks."
The government source denied all allegations of torture.
"Anyone who is arrested is taken in after a warrant issued by the public prosecution which, alongside the courts, oversees all detention facilities. Anyone who claims they are being mistreated can file a complaint with the prosecutor or the court and they will punish anyone guilty of torture."
Many Egyptians support Sisi for delivering a degree of stability after years of turmoil following the 2011 uprising that ousted Hosni Mubarak.
JOURNALISM IS OVER
The crackdown on press freedom, which other than imprisonment also includes heavy restrictions on journalists, has left entire regions "severely underreported," CPJ said.
This has been most notably the case in the Sinai Peninsula, CPJ said, where the army is battling an insurgency that has killed hundreds of policemen and soldiers since the army toppled Islamist President Mohamed Mursi after mass protests against his rule in 2013.
Balshy also noted that "terrorist groups" threatened the lives of any who spoke out against them.
Journalists are regularly denied entry to Sinai at military checkpoints, CPJ said, and local reporters face threats from both the government and militant groups.
"This reflects a denial of the security situation on the ground in Sinai, where military operations are taking place to fight terrorism," said the government source.
He added that when journalists are prevented from entering Sinai it is done for security reasons and out of fear for the safety and lives of journalists.
"Journalism is over in the Sinai," CPJ quoted one North Sinai reporter, who declined to be named for security reasons. "The only reporting we can do is (to) tell the army's story. Anything else is a prison wish." (Editing by Yara Bayoumy and Larry King)