Alexander Alexandrov and Yevgeny Yerofeyev have acknowledged being Russian servicemen and said they were on a reconnaissance mission. Russia's Defence Ministry, however, said they had resigned from active duty in December.
Russia has denied sending troops to Ukraine, where Russia- backed separatists have been fighting government troops since April 2014. At least 8,000 people have been killed in the conflict.
Yerofeyev told journalists during a break in today's court session he was under constant pressure from investigators to provide information.