VATICAN CITY (AFP) - The Vatican has long played global mediator but has struggled to make its mark in the Ukraine conflict, walking a tightrope between its desire for peace and ties with the Russian Orthodox Church.

With a self-proclaimed "willingness" to help in the negotiations, Pope Francis' unprecedented visit to the Russian embassy and high-level phone calls, the Holy See has spared no effort since Russia invaded Ukraine last month to achieve a ceasefire.

But despite past successes, notably in the historic rapprochement between Cuba and the United States in 2014, its attempts to play peacemaker in the Ukraine conflict have yet to yield results.

This is because, analysts say, the Argentine pontiff has been forced to perform a diplomatic balancing act.

He has been drawn into the conflict as the spiritual guide of five to six million Catholics in Ukraine.

But the Vatican has also spent years fostering closer ties with the Russian Orthodox Church, led by Patriarch Kirill - a close ally of President Vladimir Putin and a key pillar of his ruling apparatus.

This led in 2016 to the historic meeting between Pope Francis and Patriarch Kirill, the first encounter by the heads of the two churches since Christianity split into Western and Eastern branches in the 11th century.

In December, the pontiff even raised the possibility of going to Moscow to meet "brother" Kirill in the near future.

The Pope "is inevitably considered as both judge and party" in the conflict, noted Mr Bernard Lecomte, a specialist in the Vatican and eastern Europe.

The result has been a series of public statements by the Pope condemning the war in increasingly emotive terms - without ever mentioning Russia as the aggressor.

Turning point

The Pope's approach has sparked criticism, which only grew following Patriarch Kirill's outspoken support of the Russian intervention, calling Moscow's opponents in Ukraine "evil forces".

Afterwards, Pope Francis stepped up his rhetoric, condemning the "unacceptable armed aggression" and the "barbarity" of the killing of innocents.

With that, "the impartial role, which is an advantage for a mediator, is reduced", noted Dr Stein Tonnesson, a member of the Peace Research Institute Oslo, who said he was "pessimistic" about the chances of the Vatican arbitrating peace talks over Ukraine.

Ms Constance Colonna-Cesari, author of the book Holy Diplomacy: The Secret Power Of The Vatican, said: "There is a real turning point - it pushes Vatican diplomacy out of its realpolitik attitude."

For his part, Patriarch Kirill is also facing protests by sections of his clergy in Ukraine, who have called for a severing of ties with the patriarchy.

Spiritual level

Alongside its diplomatic efforts, the Vatican has played its traditional humanitarian role, sending cardinals to the region and activating refugee networks.

And the Pope has emphasised the importance of religious dialogue.

On Wednesday (March 16), during a video call with Patriarch Kirill, Pope Francis said the Catholic Church "must not use the language of politics, but the language of Jesus", saying both men should "unite in the effort to help peace".

For Vatican watchers, this was an attempt by the Pope to take the discussion back to a subject that drives him - closer relations between different faiths.

The pontiff "has an interest in confining himself to the spiritual, to use values, symbols... without talking politics, which would discredit him immediately", said Mr Lecomte.

On Friday, the Pope invited bishops from around the world to take part in a ceremony on March 25 for Russia and Ukraine in St Peter's Basilica.

"As long as we remain on a spiritual level, there will be a sliver of possibility of dialogue. We know from history that these channels, at a certain moment, can be very precious," said Mr Lecomte.