The amendments constitute a change of the state system, for which there is "no justifiable and acceptable reason or necessity," a statement from the presidency said.

The president sent the package back to parliament for reconsideration. If the legislature passes the amendments for a second time without change, Sezer must either approve them or submit them to a referendum.

The package was rushed through parliament earlier this month by the governing Islamist-rooted Justice and Development Party (AKP) after a political crisis blocked the election by parliament, as the current law requires, of its presidential candidate, Foreign Minister Abdullah Gul.

Sezer, who has often clashed with the government, said the amendments would lead to "a deviation from the parliamentary system" and "create far-reaching, irreparable problems for having been enacted in such a short time and without debate."

Prime Minister Recep Tayyip Erdogan has already said the government will push for the amendments to be voted through a second time if rejected by the president.