VILNIUS, Dec 13 (Reuters) - Belarusian President Alexander Lukashenko freed 123 prisoners on Saturday including Nobel Peace Prize winner Ales Bialiatski and leading opposition figure Maria Kalesnikava in a deal brokered by an envoy for U.S. President Donald Trump. In return, the U.S. agreed to lift sanctions on Belarusian potash. Potash is a key component in fertilisers, and the former Soviet state is a leading global producer. The prisoner release was by far the biggest by Lukashenko since Trump's administration opened talks this year with the veteran authoritarian leader, a close ally of Russian President Vladimir Putin. Western governments had...