Turkey's main opposition party u. Hundreds of demonstrators marched in a central neighbourhood, clanking pots and pans and chant.
On Monday, Kremlin spokesman Dmitry Peskov told reporters that the results of Turkish referendum should be respected.
The Turkish government has been widely condemned by Western nations for its repression of opposition figures following a failed military coup previous year.
The decision upholds the result of the landmark referendum, which has polarised Turkey in the last few months and highlighted the splits in a society that is still reeling from a coup attempt a year ago and repeated terror attacks by Islamic State and Kurdish separatists.
Separately, Foreign Minister Sebastian Kurz said that after the Turkish referendum, "we can no longer simply return to business as usual".
To the dismay of opposition parties and "No" supporters, the YSK made a last-minute decision on Sunday to accept ballot papers in envelopes without an official stamp.
Also, the Organisation for Security and Co-operation in Europe said earlier that the Turkish referendum took place on "an unlevel playing field".
German Chancellor Angela Merkel also warned that the "tight referendum result shows how deeply divided Turkish society is and that means a big responsibility for the Turkish leadership and for President Erdogan personally".
However, the CHP challenged the result. Questions about whether Erdogan's government abused the process to ensure its preferred outcome remain unanswered.
Republican People's Party leader Kemal Kilicdaroglu accused the electoral board of bias and of favoring the governing party. It cited precedents in which it had accepted unstamped ballots as valid due to the incompetence or lack of training of local ballot box officers who had failed to stamp them in time for elections.
His prime minister - whose post is being abolished under the changes - said "rumours of irregularities" were an effort to cast a shadow over the result.
CHP vice chairman Erdal Aksunger said the party expects the board "to eliminate fraud and cancel the referendum".
Istanbul police on Wednesday detain 16 leftist activists involved in demonstrations against the "Yes" victory in the referendum on expanding President Recep Tayyip Erdogan's powers, a laywer says.
Turkish President Recep Tayyip Erdogan has apparently realized his vision for turning his nation from a parliamentary democracy to a new system of government where a strong executive - Erdogan himself - wields overwhelming power.
The new system takes effect at the next election, now slated for November 2019. This would allow Erdogan to rejoin the governing AKP he co-founded, or to lead it.
In their petitions Tuesday, the residents of Ankara said the decision and other reported irregularities were in open violation of the law. As I said this will come before the parliament and if it is passed from the parliament, I would approve this. "We share our report and we completed our mandate".
He also warned against further antagonizing Ankara, saying it was not in the EU's interest to see Turkey moving closer to Russian Federation.
Trump and Erdogan spoke via phone on Monday in a pre-arranged call, in which the US President offered congratulatory words, as well as discussing topics such as the ongoing conflict in Syria.
The White House readout of Mr Trump's call noted the pressing issues on which the U.S. has tried to work with Turkey, namely fighting the so-called Islamic State group and quelling Syria's civil war.
Bilginsoy contributed from Istanbul and Mehmet Guzel contributed from Ankara.