(CNN) -- Dozens of international correspondents came together Monday to demand that Egypt release three journalists they say have been detained arbitrarily for two weeks.
Peter Greste, Mohamed Fadel Fahmy and Baher Mohamed from Al Jazeera English were arrested by Egyptian authorities on December 29 and have been held since.
Egyptian authorities say the journalists held illegal meetings with the Muslim Brotherhood, which was declared a terrorist group last month.
There has been a crackdown on the Islamist movement, and ensuing political turmoil, since the army ousted Mohamed Morsy, Egypt's first democratically elected President, in July.
In a show of solidarity, nearly 40 correspondents and editors representing 29 international media organizations sent a letter to the Egyptian authorities to demand the journalists' immediate release.
The letter was signed by Christiane Amanpour, CNN chief international correspondent and a member of the board of the Committee to Protect Journalists; BBC chief international correspondent Lyse Doucet; and reporters and editors for NPR, The Washington Post, Le Monde, France 24 and The Economist, among other news outlets.
"We are deeply concerned to learn that our colleagues, all three of whom are well respected journalists, may face charges that include belonging to a terrorist organization and spreading false news that could endanger national security," the journalists say in the letter.
They also call for the release of other journalists who have been detained in Egypt, some of whom they say have been arbitrarily imprisoned for more than five months.
"The arrest of these journalists has cast a cloud over press and media freedom in Egypt," the letter reads.
"We strongly believe that upholding the rights of journalists and permitting the free flow of information is vital to bringing about greater understanding and serves the best interests of all Egyptians and the world."
Highly charged environment
Originally, four Al Jazeera journalists were detained last month, but the Egyptian government released cameraman Mohamed Fawzy on December 31.
The Egyptian Interior Ministry said on its Facebook page that security forces arrested a Muslim Brotherhood member and an Australian journalist at a Cairo hotel. Greste, an Australian, previously worked for CNN, Reuters and the BBC.
Fahmy worked for CNN and The New York Times before joining the Qatar-based network; Mohamed is a Cairo-based producer for the network.
The ministry said the Muslim Brotherhood member used the hotel to meet with other members and as a media center to broadcast damaging news about the government for Al Jazeera.
Calling the arrests arbitrary, Al Jazeera has said the network "has been subject to harassment by Egyptian security forces," including having its equipment confiscated and offices raided, despite the network not being banned from working in Egypt.
Observers say Egypt's media environment has been highly charged since Morsy's overthrow.
Several Islamist channels were closed down immediately after the military intervention in the summer.
The arrests occurred the day before the Committee to Protect Journalists issued a report saying Egypt, Syria and Iraq have become the deadliest countries for journalists.
Seventy journalists were killed in 2013, with six of those deaths in Egypt, the CPJ said.
Since Morsy's ouster, the Arab world's most populous nation has seen months of political turmoil as an interim military-backed government has taken charge.
Hundreds died in clashes between Egyptian security forces and Morsy supporters in the weeks that followed his ouster.
Detractors say Morsy was a tyrant trying to impose conservative values, but his supporters say the military has returned to the authoritarian practices of longtime ruler Hosni Mubarak, who was deposed in a popular uprising in 2011.
Egypt is now preparing to hold a referendum Tuesday and Wednesday on a new constitution that would ban religious parties and put more power in the hands of the military. If the constitution is passed, elections should follow.