Polish bishop Jerzy Mazur was declared persona non grata and put on a plane back to Warsaw when he arrived in Moscow in April, an incident that aggravated already strained relations between the Vatican and the Russian Orthodox Church.
"The pope took it upon himself to write personally to Putin and ask him to intervene personally so that the pastor ... can return to his Catholic community in a remote corner of the Russian Federation," Vatican Foreign Minister Jean-Louis Tauran told Vatican radio in an interview.
"President Putin has not yet answered the pope. The pope's letter was dated May 8," he added.
It is the second letter the church has addressed to Russian authorities about the case. Tauran said a communique he sent earlier to Foreign Minister Igor Ivanov was also not answered, according to a transcript of the interview.
Mazur, who had worked at a diocese in Irkutsk since 1998, was at a loss to explain in April why he thought Russian authorities had banned him from the country, saying he had not knowingly broken the law in any way.
The incident prompted Poland to summon Moscow's ambassador to demand an explanation, while Russia defended its decision on the basis of "serious complaints about the activities of the Vatican's senior representative," without elaborating.
"I think, above all, it is important for the Russian authorities to acknowledge the seriousness of the situation," Tauran said, playing down suggestions Putin's failure to respond to the pope constituted a "diplomatic incident."
The Polish-born Pope, now 82 and in declining health, wants to heal the schism that has existed between the two churches since 1054 and visit Russia. The Orthodox establishment has treated his overtures as a threat, accusing Rome of "poaching" believers on its own soil. Russia's Catholics, many descended from Poles deported to Siberia in World War II, are thought to number about 600,000 in a population of 140 million.
Tauran arrived in Ukraine on Saturday to commemorate the pope's first visit to the country one year ago, The Associated Press reported.
He was expected to meet with President Leonid Kuchma and Foreign Minister Anatoly Zlenko in Kiev before leaving for Lviv, a city near the Polish border.