Patriarch Kirill, the leader of the Russian Orthodox Church, called on Russian and Ukrainian naval personnel in the Crimea to cooperate peacefully, during his visit to Sevastopol on Sunday.
Kirill arrived on the peninsula, where Russia has a naval base, on Friday as part of his 10-day visit to Ukraine.
After laying flowers at a WWII memorial, the patriarch gave a speech to a crowd of several thousand locals, along with service personnel from the Russian and Ukrainian navies.
"There are two fleets here, not one, but in both of them serve brothers in faith."
"Today, my prayer was that these brothers never look at each other down the sights of guns, but help each other in the most difficult of political and economic circumstances," he said.
He said he felt sure that his prayer is supported by those who died defending Sevastopol.
The presence of Russia's Navy in southern Ukraine remains a major source of tension between the two countries.
Russia's Black Sea Fleet uses a range of naval facilities in the Crimea, including the main base in Sevastopol, as part of a 1997 agreement, under which Ukraine agreed to lease the bases to Russia until 2017.
Although the agreement on Russia's use of the base foresees a possible extension of the lease, and Moscow has repeatedly said it wants negotiations on the issue, Ukraine's leadership insists that it will not permit an extension of Russia's naval presence in the country after 2017.
Ukrainian President Viktor Yushchenko announced last summer that Ukraine would not extend the lease of the Sevastopol base, and urged the Russian fleet to start preparations for a withdrawal.