As military units patrolled the streets and seized key bridges, the Turkish military declared martial law Friday and said in a statement read out on Turkish television that it had "fully seized control" of the country.

In response, Turkish President Tayyip Erdogan, speaking from an undisclosed location, surfaced via FaceTime on CNN Turk calling on the Turkish people to take to the public squares and go to the airport.  "I've never seen anything more powerful than the people," he said.

The president's office would not reveal Erdogan's whereabouts, saying only that he is at a secure location.

A senior U.S. military source tells NBC News that Erdogan, refused landing rights in Istanbul, is reported to be seeking asylum in Germany. The report could not immediately be independently confirmed.

As both sides claimed the upper hand, Turkish Prime Minister Binali Yildirim challenged the military's claim that it was in charge, saying only that there had been "an uprising," according to the Hurriet Daily News.  He said Turkey would never allow any "initiative that would interrupt democracy."

ANKARA, TURKEY - JULY 15: Supporters of Turkish President Recep Tayyip Erdogan chant slogans on the main streets on July 15, 2016 in Ankara, Turkey. Istanbul's bridges across the Bosphorus, the strait separating the European and Asian sides of the city, have been closed to traffic. Reports have suggested that a group within Turkey's military have attempted to overthrow the government. Security forces have been called in as Turkey's Prime Minister Binali Yildirim denounced an 'illegal action' by a military 'group', with bridges closed in Istanbul and aircraft flying low over the capital of Ankara (Photo by Kutluhan Cucel/Getty Images)
ANKARA, TURKEY - JULY 15: Supporters of Turkish President Recep Tayyip Erdogan chant slogans on the main streets on July 15, 2016 in Ankara, Turkey. Istanbul's bridges across the Bosphorus, the strait separating the European and Asian sides of the city, have been closed to traffic. Reports have suggested that a group within Turkey's military have attempted to overthrow the government. Security forces have been called in as Turkey's Prime Minister Binali Yildirim denounced an 'illegal action' by a military 'group', with bridges closed in Istanbul and aircraft flying low over the capital of Ankara (Photo by Kutluhan Cucel/Getty Images)

Supporters of Turkish President Recep Tayyip Erdogan chant slogans on the main streets on July 15, 2016 in Ankara, Turkey.

Photo Credit: Kutluhan Cucel/Getty Images

Meanwhile, Turks poured out into the streets despite the sound of explosions and gunfire in Istanbul.

In Ankara, the U.S. Embassy issued an emergency message reporting that many bridges had been shut down in Istanbul and that shots have been heard in Ankara. It said the government claimed that its security forces were taking action to contain it.

"We encourage U.S. citizens to shelter in place and do not go the U.S. Embassy or Consulates at this time," the embassy said. "Monitor local press for updates, avoid areas of conflict, and exercise caution if you are in the vicinity of any military or security forces." The U.S. Air Force operaes out of the Incirlik Air Base in south central Turkey.

U.S. troops in Turkey haven't been affected, a spokeswoman for U.S. Air Forces in Europe said in a statement. "We are aware of media reports of the attempted coup in Turkey. Currently, this has no impact on Incirlik AB."

Separately, the Pentagon released a similar statement. "We are monitoring the situation in Turkey closely and are taking appropriate steps to ensure the safety and security of our service members, civilians, their families, and our facilities. As of this time, there has been no impact to Incirlik Air Base and counter-ISIL air operations from Incirlik continue."

NBC News reported later that the threat level at Incirlik has been raised to "delta."

Turkish soldiers block Istanbul's iconic Bosporus Bridge on Friday, July 15, 2016, lit in the colours of the French flag in solidarity with the victims of Thursday's attack in Nice, France. A group within Turkey's military has engaged in what appeared to be an attempted coup, the prime minister said, with military jets flying over the capital and reports of vehicles blocking two major bridges in Istanbul. Prime Minister Binali Yildirim told NTV television:
Turkish soldiers block Istanbul's iconic Bosporus Bridge on Friday, July 15, 2016, lit in the colours of the French flag in solidarity with the victims of Thursday's attack in Nice, France. A group within Turkey's military has engaged in what appeared to be an attempted coup, the prime minister said, with military jets flying over the capital and reports of vehicles blocking two major bridges in Istanbul. Prime Minister Binali Yildirim told NTV television: "it is correct that there was an attempt," when asked if there was a coup. (AP Photo/Emrah Gurel)

Turkish soldiers block Istanbul's iconic Bosporus Bridge on July 15, 2016, lit in the colors of the French flag in solidarity with the victims of Thursday's attack in Nice, France.

Photo Credit: Emrah Gurel/AP

There have been three successful coups in Turkey, a NATO ally, since 1960, and in 1997 the military carried out a "soft" coup, issuing directives to the Turkish government that it was forced to accept. The military has cast itself as the traditional protector of secular, democratic rule.

As the coup attempt unfolded, security forces in Istanbul blocked two bridges connecting the Anatolian side to the European side of the city. Travelers reported on their Twitter accounts that airliners were stopped from taking off, while military aircraft were seen flying over Ankara, the capital.

Dogan News Agency reported that police in Ankara called personnel to their officers. In addition, media reports said ambulances were seen in front of the Turkey's military headquarters.

State-run Anadolu Agency is reporting that Chief of General Staff Hulusi Akar is being kept as a hostage, according to Hurriet Daily News.

The U.S. State Department said on Twitter in a report to American travelers that it was "confirming media reports of gunshots & possible attempted uprising in Turkey. Remain vigilant." Social media — including Twitter, and Facebook —were all blocked in the country.

CNNTürk reported that the coup attempt got underway in Ankara when two busloads of soldiers entered the headquarters of the state-run TRT news agency, and that the channel then started to broadcast a stream of weather forecasts, Hurriet reported.

The Turkish military statement was read out by the normal news anchor on TRT television, saying the military had taken action "to reinstall the constitutional order, democracy, human rights and freedoms, to ensure that the rule of law once again reigns in the country, for the law and order to be reinstated," the private Dogan agency reported.

The military said that "all international agreements and commitments will remain. We pledge that good relations with all world countries will continue."

The anchor said the statement was issued in the name of a so-called "peace council," according to a local resident.

Meanwhile, the head of the ruling Justice and Development Party's (AKP) in a phone call with CNNTürk called on citizens to hit the streets, saying that a group of soldiers were trying to take him and other party members out of the building, Hurriet reported.

Contributing: Oren Dorell in Washington and Michael Burke in McLean,Va., for USA TODAY; Air Force Times reporter Oriana Pawlyk