The Turkish authorities have seized control of the Cihan news agency, expanding the crackdown against supporters of the Muslim cleric Fethullah Gulen, who is an influential critic of President Tayyip Erdogan, the news agency said. At the request of a state prosecutor, a court in Istanbul will appoint an administrator to run the news agency, Cihan reported on its website late Monday. The action came a few days after the authorities seized control of the newspaper Zaman, which is also linked to Mr. Gulen, who is living in the United States. A State Department spokesman, John Kirby, on Tuesday called the seizing of Cihan was “another example of an unnecessary crackdown on journalism,” and he urged the Turkish government to ensure full respect for due process. The government has accused Mr. Gulen, a former ally of the president, of conspiring to overthrow the government by building a network of supporters in the judiciary, police and news media. Mr. Gulen has denied the accusation.