Czech President Milos Zeman was quoted as saying, Censor.NET reports citing Reuters.
"An annexation means breaching international agreements and it is doubtless that agreements guaranteeing Ukraine's territorial integrity were breached," Zeman said in a response to a reader's question published by www.parlamentnilisty.cz.
"On the other hand, I agree with you that (Soviet leader Nikita) Khrushchev made an unforgivable silly thing and world's politicians acknowledge today that Crimea cannot be given back to Ukraine," Zeman said. He did not specify who those politicians were.
Khrushchev gave Crimea to Ukraine, then part of the Soviet Union, in 1954.
The Czech government, which has the main say in the foreign policy of the EU country, has followed the common stance of the bloc regarding the sanctions on Russia.
Russia annexed Crimea, which includes the strategic port of Sevastopol where its Black Sea Fleet has been based, in 2014, prompting the European Union and United States to impose economic and political sanctions on various Russian companies and officials.
Zeman has spoken out against the EU sanctions and has regularly expressed pro-Russian views. He was the only Western leader to attend the May 2015 celebrations in Moscow to mark the end of World War Two.
The United States expanded its sanctions over the Crimea annexation on Sept. 1, adding dozens of people and companies, some of them involved in building a multi-billion dollar bridge to link the Russian mainland with the peninsula.