In a press conference at Istanbul's Ataturk Airport, Erdogan said the architects of the coup attempt would "pay a heavy price" and vowed he would "not surrender this country to intruders."

Prime Minister Binali Yildirim, speaking to state-run Anadolu Agency, said more than 120 arrests had been made.

Despite claims by multiple Turkish government officials that the takeover attempt had been repelled, reports of ongoing violence indicated that authorities did not have full control of the situation.

The Ankara prosecutor's office said at least 42 people had been killed in "attacks" in the capital. At least 17 of the victims were police officers killed in a helicopter attack on police special forces headquarters in Ankara. An official at Haydarpasa Numune Hospital in the Uskudar district of Istanbul told The Associated Press they had admitted at least 150 wounded, but declined to comment on whether there had been any fatalities.

Despite stating that the plotters were "a minority within the military," Erdogan also admitted that his general secretary was abducted by coup makers and that he did not know the whereabouts of the chief of the military staff. The president also said that his vacation residence in the holiday resort of Marmaris had been bombed earlier that evening.

A Turkish lawmaker contacted by Reuters said he and his colleagues were hiding in special shelters in the bowels of the parliament building after at least three explosions near the complex in the capital, Ankara.  Parliament Speaker Ismail Kahraman told the Associated Press a bomb hit one corner of a public relations building inside the parliament complex, injuring some police officers.

Elsewhere, gunfire and explosions were reported in several areas of Istanbul, including Taksim Square, which occasionally has been a center of protest against Erdogan. 

A Turkish government spokesman confirmed that an F-16 fighter had shot down a helicopter that had been commandeered by soldiers supporting the coup. Anadolou reported that military helicopters also attacked the headquarters of TURKSAT satellite station on the outskirts of Ankara.

CNN Turk reported that soldiers had entered its offices in Istanbul and cut off its broadcast. An anchor said, "We must abandon the studio, we tried to broadcast everything until the last minute... and I am being asked to leave the studio." A camera showed an empty anchor desk as chants of "Soldiers out!" could be heard inside and outside the studio. The channel later resumed normal programming.

Earlier, the state-run television broadcaster TRT was similarly knocked off the air, but later came back online. 

Earlier, Reuters reported that tanks surrounding the parliament building had opened fire. The Turkish news agency Dogan reported that soldiers had opened fire on people who were crossing Istanbul's Bosporus Bridge to protest the coup attempt and some people had been wounded.

Dozen of tanks were seen moving toward a palace that is now used by the prime minister and deputy prime ministers. A civilian car tried to stop one of the tanks, but it rammed through the vehicle as those in the car escaped.

Speaking by cell phone to CNN Turk from an unknown location in the early hours of the coup, Erdogan vowed that Turkey would "overcome this invasion" and called on Turks to "gather in squares and see what this minority can do with their tanks and artillery against the people."

Ordinary Turkish citizens appeared to heed Erdogan's call, as TV footage showed marching through the streets of Izmir and Istanbul waving Turkish flags. Crowds also gathered in Ankara's main square.

Earlier in the evening, the Dogan news agency reported that soldiers had entered Ataturk Airport's control tower and stopped all flights. Several military vehicles were seen outside the airport's terminals, which were attacked by Islamic extremists last month. 

"Throughout history those who make coups have been unsuccessful, and I absolutely believe that these will be unsuccessful as well," Erdogan said, adding that the architects of the takeover attempt "will absolutely pay the price for this in heaviest manner."

In Washington, a statement from the White House said President Barack Obama and Secretary of State John Kerry agreed that both sides "should support the democratically elected government of Turkey, show restraint and avoid any violence or bloodshed."

A senior Defense Department official told Fox News that the unrest was having "no impact" on anti-ISIS missions flown out of Incirlik Air Base in southeastern Turkey.

NATO Secretary General Jens Stoltenberg issued a statement calling for "calm and restraint, and full respect for Turkey's democratic institutions and its constitution."

A military statement read on Turkish state TV announced that martial law had been imposed across the country and a curfew had been declared. The statement added that Turkey was now being run by a "peace council" and that a new constitution would be drawn up soon.

However, at least one senior military leader refused to back the coup attempt. 

"Those who are attempting a coup will not succeed. Our people should know that we will overcome this," Gen. Zekai Aksakalli, the commander of the military special forces, told the private NTV television by telephone.

The coup began shortly before 11 p.m. local time Friday, when gunshots were first reported in Ankara. As military helicopters flew over the entertainment hub of Beyoglu district in Istanbul, televisions aired footage of military tanks and TV stations reported Turkish state TV TRT had been taken over by military officials.

Prime Minister Binali Yıldırım admitted to Haberturk TV that an "attempt” had been made against the government and warned "those who carry out this attempt will be subjected to heaviest punishment.”

Turkey’s Justice Minister Bekir Bozdag also spoke on national TV, calling on "everyone to raise their voices against this attempt by the military and to embrace democracy.”

Ambulances were seen in front of Turkish military headquarters amid early reports that hostages were being held there.

Soldiers and military vehicles also blocked one-way traffic on the Bosporus and Fatih Sultan Mehmet bridges in Istanbul, which link the continents of Europe and Asia.

The chaos capped a period of political turmoil in Turkey blamed on Erdogan's increasingly authoritarian rule, which has included a government shake up, a crackdown on dissidents and opposition media and renewed conflict in the mainly Kurdish areas of the southeast.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.