Tens of thousands of people have joined a pro-democracy rally in Istanbul, condemning the nation's attempted coup.
Obama also flatly rejected claims that the USA had prior intelligence of the July 15 putsch attempt, calling such suggestions "unequivocally false".
Some members of the air force were involved in the coup attempt, during which Akar was held hostage.
The official number of those in custody since the Jul 15 putsch has surged above 13,000 soldiers, police, justice officials and civilians in a wave of arrests that has alarmed North Atlantic Treaty Organisation allies and European leaders.
He told France 24 on Saturday that Turkey has no choice but to impose stringent security measures after the attempted coup was put down by loyalist forces and civilian protesters.
Gulen has condemned the attempted coup and denied any involvement in it. Obama, reiterating what United States officials had said earlier this week, said he told Erdogan his government must first present evidence of Gulen's alleged complicity in the failed coup.
Mr. Brennan, said, "We..." and then laughed awkwardly before continuing. He pledged they would have a fair trial.
Amnesty has said Mr Erdogan is going "well beyond what might be considered a legitimate response to the coup attempt".
Turk Telekomunikasyon AS, the country's largest telephone operator, said in a statement Sunday that some of its executives were detained and that the company is cooperating with investigators.
The decree extends from four to 30 days the period in which suspects can be detained.
But for now, the crackdown appears to be broadly popular.
Gulen and his supporters have said the government is using the state of emergency "to solidify his power and persecute his critics". "If people lost their jobs they must be guilty".
"I can not overstate the sense of the Turkish government and the Turkish people right now that they truly felt and truly feel under threat", State Department spokesman Mark Toner told an Associated Press reporter at a department briefing.
"The government has to think about the mistakes they have made they have to think about the other half of the population". "We all have to come together".
The failed coup was led by Col. Muharrem Kose, a former Turkish military officer who was dishonorably discharged in March 2016 for his alleged association with anti-government and US-based dissident Fethullah Gulen.
The first decree authorises the closure of 1043 private schools, 1229 charities and foundations, 19 trade unions, 15 universities and 35 medical institutions over suspected links to the Gulen movement, the Anadolu agency said. It was joined by other opposition parties and President Tayyip Erdogan's Islamic Justice and Conservative Party (AKP), which has ruled Turkey since 2002.
As well, given the coup more than 3000 soldiers have been arrested.
Turkey's secular Republican People's Party, CHP, has planned a rally for Sunday.
He said: "The state can not be governed by grudge, anger and prejudice".
Turkey's Supreme Military Council (YAS) will meet under Erdogan's supervision on July 28.