Merkel told the RedaktionsNetzwerks Deutschland (RND) that Russia had caused a major crisis by annexing the Black Sea peninsula of Crimea in 2014 and with its support for separatists in eastern Ukraine.
"Europe had to react against this violation of basic principles," Reuters quoted Merkel as saying.
She added that she and French President Francois Hollande were working "with all one's strength" to urge Ukraine and Russia to implement the so-called Minsk ceasefire agreement despite all the difficulties.
Russia has been under US and EU sanctions over its annexation of Crimea and support for separatists in eastern Ukraine for two years.
The EU agreed in June to extend energy, financial and defense sanctions on Russia over the conflict in Ukraine until the end of January next year.