The owner, Burak Akbay, and the three others, including the executive in charge of the website Mediha Olgun, are accused of links to the religious sect led by US-based Islamic preacher Fethullah Gülen, one of the masterminds of last year's failed coup.
The charges against the four suspects included planning "the assassination of the President and physical assault" and "armed rebellion against the government of the Turkish Republic".
Police carried out searches at the homes of the owner and the three employees of Sözcü, which is critical at times of President Recep Tayyip Erdoğan and his ruling AKP party.
The investigation drew sharp criticism from Turkey's main opposition party CHP. Its leader, Kemal Kılıçdaroğlu, said the operation against Sözcü was unacceptable and called on the judiciary to act. "Turkey cannot take this pressure on the media," he said.
The daily issued a statement of defiance on its website: "Let no one have any doubt, Sözcü will not be silent. It will continue to be the voice of this country's conscience."
The Turkish Journalists’ Association also released a statement on the operation, declaring “solidarity” with Sözcü’s staff.
