Sannikau's relatives say KGB officials refused on March 7 to accept a package with food and gifts for him.
Sannikau is charged with organizing mass unrest on Minsk's Independence Square on December 19. He and several other opposition presidential candidates, along with hundreds of their supporters, were arrested in Belarus on December 19-20 while protesting the results of the presidential election, which they say was rigged.
Incumbent President Alyaksandr Lukashenka was named the runaway winner of the vote, which international election monitors said was flawed.
Two other former presidential candidates -- Sannikau and Mikalay Statkevich -- remain in custody. Another, Uladzimer Nyaklyaeu, is under house arrest and yet another, Ales Mikhalevich, is banned from leaving Minsk.
All have been charged with organizing mass unrest.
Sannikau's wife, Iryna Khalip, has also been charged with organizing mass unrest on December 19-20 in Minsk. She was arrested and jailed together with Sannikau on December 19. Khalip was released from detention and placed under house arrest on January 30.
Sannikau's lawyer, Paval Sapelka, was disbarred on March 3. Two lawyers who had agreed to defend Khalip last month suddenly refused to take up her case. They were later also disbarred by Belarusian officials.
Read more in Belarusian here