The YSK stated on April 19 that it inspected appeals from the two parties in parliament, as well as the Vatan Party, and rejected them all, with only one affirmative vote from its 11 members.
But the tight result of a highly charged campaign laid bare divisions, while European observers and the head of Turkey's bar associations union said a decision to count unstamped votes broke electoral law.
Both the main opposition Republican People's Party (CHP) and the Kurdish issue-focused Peoples' Democratic Party (HDP), the third largest party in parliament, had submitted legal objections to the board, mainly due to its decision to not deem ballot papers without official seals invalid.
Turkey's High Electoral Board rejected on Wednesday appeals to from the main opposition parties to annul the referendum granting President Recep Tayyip Erdogan sweeping new powers, the board said in a statement.
She vowed that her party will "not recognise" the referendum result, arguing that the referendum process was fraudulent and the results were manipulated.
Before the announcement, Prime Minister Binali Yildrim said the opposition had the right to file objections but said that calling for street protests was unacceptable. "We will employ all legal ways available", Tezcan said.
A prosecutor will now consider whether to press charges against Guven.
He said that "the path to seek rights" should be limited to the courts.
"Calling people to the street is wrong and is outside the line of legitimacy", Yildirim said, adding, "we expect the main opposition party's leader to act more responsibly".
The protesters on Wednesday evening chanted "Thief, Murderer, Erdogan" and "Don't be silent, shout out, "no" to the presidency".
Global election monitors, including the Organisation for Security and Cooperation in Europe, have expressed concern over the way the vote was carried out. "From the German government's point of view, Turkey must. clear up the questions that have been raised".
Anadolu news agency cited a statement by Istanbul Police that said the suspects were detained early Wednesday for attempting to provoke a response similar to the mass anti-government demonstrations that happened across Turkey in 2013.
"That the Turkish leadership didn't like the criticism by the OSCE's election observer mission isn't a surprise to anyone", German Foreign Ministry spokesman Martin Schaefer said.
Turkish President Tayyip Erdogan will meet U.S. President Donald Trump in May ahead of a meeting of the North Atlantic Treaty Organisation alliance, Turkish Foreign Minister Mevlut Cavusoglu said on Wednesday.