Erdogan won another five years in office in Sunday's vote and immediately pledged to implement changes that boost his authority, which opponents fear will give him autocratic powers.

Turkey is an important member of NATO because of its strategic location bordering Iraq and Syria and close to Russia, and has played a key role in the fight against the Islamic State group in the Middle East.

But there have been tensions with other alliance members, notably over Erdogan's rapprochement with Moscow, signing a deal to buy Russian air defence missiles, and with the US over the role of Kurdish fighters in the battle against IS.

"I will congratulate President Erdogan on his re-election as president. I also congratulate the Turkish people on the high turnout in the elections," Stoltenberg said as he arrived for a meeting with EU foreign and defence ministers in Luxembourg.

A sweeping crackdown after a failed coup to unseat Erdogan has alarmed many Western countries, with tens of thousands of people arrested.

"NATO is based on some core values: democracy, the rule of law, individual liberty. I personally attach great importance to these values and I underline the importance of these values in many different NATO capitals including Ankara when I met Turkish leaders there," Stoltenberg said.