Ukrainian President Petro Poroshenko on Monday signed into law a controversial language bill which has sparked a standoff with Romania and other east European states.
The law states that starting in September 2020, students will be taught exclusively in Ukrainian from the fifth grade onwards, though they can still learn their native languages as a separate subject.
But Romanian President Klaus Iohannis has said the bill "drastically limits" the access of minorities to education in their native language, and cancelled a planned trip to Kiev this month.
The legislation has also raised hackles in Ukraine's sizable Hungarian and Polish minorities.
A statement issues by the presidency said Poroshenko "especially stressed that the law raises the role of Ukrainian as a state language in the education process."
"The law ensures equal opportunities for all," it added.
"It guarantees every graduate strong language skills essential for a successful career in Ukraine."
But ethnic Russians account for Ukraine's biggest minority and the language issue has further inflamed Moscow's relations with Kiev.
Several Ukrainian regions, especially those in the east, are mainly Russian-speaking, and the Kremlin claims the Ukrainian authorities are seeking to sideline the Russian language and its people.
But Poroshenko said his county was abiding by all international norms.
The language law "is in harmony with European standards and is an example for neighbouring countries," the presidency quoted Poroshenko as saying.