WASHINGTON, April 1 (Reuters) - The United States on Monday accused Egypt of muzzling freedom of speech after prosecutors questioned the most popular Egyptian television satirist over allegations he insulted President Mohamed Mursi and Islam.

U.S. State Department spokeswoman Victoria Nuland also suggested the Egyptian authorities were selectively prosecuting those accused of insulting the government while ignoring or playing down attacks on anti-government demonstrators.

Bassem Youssef, who rose to fame with a satirical online show after the uprising that swept autocrat Hosni Mubarak from power in 2011, turned himself in on Sunday after the prosecutor general issued an arrest warrant for the comedian on Saturday.

Youssef, whose program is now on television and has been compared to U.S. satirist Jon Stewart's the Daily Show, is accused of insulting Islam and undermining Mursi's standing.

"We have concerns that freedom of expression is being stifled," Nuland told reporters at her daily briefing, citing Youssef's arrest and his subsequent release on bail of 15,000 Egyptian pounds ($2,200) on Sunday.

In what seemed a gesture of defiance, Youssef arrived at the prosecutor general's office on Sunday wearing an oversized graduation hat modeled on one donned by Mursi when he was awarded an honorary degree in Pakistan in March.

The prosecutor general issued the warrant after at least four legal complaints filed by supporters of Mursi, a Muslim Brotherhood politician who was freely elected last June.

Referring to Youssef's case, Nuland added: "This, coupled with recent arrest warrants issued for other political activists, is evidence of a disturbing trend of growing restrictions on freedom of expression."

"The government of Egypt seems to be investigating these cases while it has been slow or inadequate in investigating attacks on demonstrators outside of the presidential palace in December 2012, other cases of extreme police brutality and illegally blocked entry of journalists," she added. "There does not seem to be an even-handed application of justice here."

Egypt has been in a state of political turmoil since the ouster of Mubarak, a long-time U.S. ally. The political uncertainty and growing street crime has deterred tourism, a key driver of the Egyptian economy.

U.S. Secretary of State John Kerry raised the issue of freedom of expression with Mursi when he traveled to Cairo in early March on his first trip since taking office and the United States will continue to press for respect of human rights, Nuland said. (Reporting By Arshad Mohammed; Editing by Paul Simao)