The European Commission called on Turkey on Tuesday to investigate alleged irregularities in Sunday's referendum boosting the powers of Turkish President Tayyip Erdogan and urged him to show restraint after his narrow victory.
Some Turkish officials said that they had expected to get much more support in favor of the constitutional amendments during the referendum, while the Turkish opposition outlined plans to appeal the results of the referendum with the country's constitutional court or the European Court of Human Rights (ECHR) if needed.
President Muhammadu Buhari has felicitated with the people and government of Turkey on the successful conclusion of the country's referendum on Monday.
Turkey's parliament has approved a three-month extension of the state of emergency declared in the wake of last year's failed coup.
Turkey rejected on Tuesday the European Union call for referendum probe.
"Saying the referendum fell below global standards is unacceptable", the ministry said in a statement, adding that previous "politically charged" comments from OSCE monitors showed the team arrived in Turkey with prejudice and disregarded principles of objectivity and impartiality.
Turkey's President Recep Tayyip Erdogan, delivers a speech during a rally of supporters a day after the referendum, outside the Presidential Palace, in Ankara, Turkey, Monday, April 17, 2017. Would we? What did England do - they did Brexit, right? But he insisted other nations' opinions on the issue were irrelevant to him. "The legal framework was inadequate for the holding of a genuinely democratic process", Cezar Florin Preda, head of the delegation from the Parliamentary Assembly of the Council of Europe, said in a statement.
USA president Donald Trump, meanwhile, ignored the concerns about voting irregularities and congratulated Mr Erdogan on his referendum victory.
Trump's congratulations on Monday were in contrast with European Union leaders who have been reserved in their reaction to the narrow victory and even his own State Department, which earlier noted concerns expressed by global observers over the "uneven playing field".
On Tuesday, the People's Republican Party (CHP), Turkey's main secularist opposition party, said it would officially file for the annulment of the referendum results with the country's High Electoral Board (YSK). In addition to discussing Erdoğan's win, the two leaders spoke about the recent US strike against a Syrian air base, which Trump thanked Erdoğan for supporting, and the continuing fight against the Islamic State (ISIS). "Turkey is sliding toward a semi-authoritarian system under one man rule".
The new system takes effect at the next election, now slated for November 2019.