PLOVDIV, Bulgaria -- Pope John Paul II, in the final act of his first bridge-building visit to Bulgaria, on Sunday beatified three Roman Catholic priests who had been executed for spying by the Communists half a century ago.

Thousands of faithful, waving Bulgarian and Vatican flags, turned out to witness the Pope leading mass on Alexander Battenberg Square, the Central Square in Plovdiv, Bulgaria's second largest city.

The three priests -- Kamen Vitchev, Pavel Djidjov and Josaphat Chichkov -- were executed in November 1952 in a Sofia prison after being convicted of espionage and plotting to wage war against Bulgaria and the Soviet Union.

"In thinking of the three new Beati, I also feel duty bound to honor the memory of the other faithful who were sons and daughters of the Orthodox Church and who suffered martyrdom under the same Communist regime," the Pope said.

The Pope first beatified a Stalinist-era martyr, Bulgarian Bishop Eugene Bossilkov, in 1998. Bossilkov was accused of crimes similar to those of the three priests and was executed at the same time.

Around 10,000 people -- including worshippers from Greece, Macedonia, Poland and Romania -- gathered to hear the leader of the world's one billion Catholics deliver mass.

The Pontiff's visit to Bulgaria, his 96th official visit, comes amid increased efforts by the Roman Catholic Church to heal a rift with the Orthodox Church, provoked by the suspicion that the Catholic Church is seeking to convert Orthodox believers in the post-Communist east.

The Catholic community in Bulgaria numbers around 60,000 -- less than one percent of the population in the former Soviet-bloc country, where four out of five people follow the Orthodox Church.

During his visit, the Pope extended several reconciliatory gestures to the Orthodox Church, offering the use of a church in Rome to the Bulgarian Orthodox community and hailing the tradition of eastern monasticism.

The Bulgarian church leader, Patriarch Maxim, had previously opposed the Papal visit but welcomed warmly the 82-year-old Pope during his stay.

Maxim maintains close relations with Russian Orthodox Patriarch Alexy II, who continues to block a long-standing Papal ambition to visit Russia.

The Pontiff returns to Rome on Sunday after his five-day journey to Azerbaijan and Bulgaria, which was undertaken despite his deteriorating health and suggestions that he should resign.