KYIV, May 29 (Reuters) - Kyiv's peace plan is the only way to end Russia's war in Ukraine and the time for mediation efforts has passed, a top aide to President Volodymyr Zelenskiy said.

Chief diplomatic adviser Ihor Zhovkva told Reuters that Ukraine had no interest in a ceasefire that locks in Russian territorial gains, and wanted the implementation of its peace plan, which envisages the full withdrawal of Russian troops.

He pushed back on a flurry of peace initiatives from China, Brazil, the Vatican and South Africa in recent months.

"There cannot be a Brazilian peace plan, a Chinese peace plan, a South African peace plan when you are talking about the war in Ukraine," Zhovkva said in an interview late on Friday.

Zelenskiy made a major push to court the Global South this month in response to peace moves from some of its members. He attended the Arab League summit in Saudi Arabia on May 19, holding talks with host Crown Prince Mohammed bin Salman, Iraq and other delegations.

He then flew to Japan where he met the leaders of India and Indonesia - important voices in the Global South - on the sidelines of the Group of Seven summit of major economic powers in Hiroshima.

While Kyiv has staunch backing from the West in its struggle against the Kremlin, it has not won the same support from the Global South - a term denoting Latin America, Africa and much of Asia - where Russia has invested diplomatic energy for years.

Moscow has bolstered ties with Global South powers during the war in Ukraine, including by selling more of its energy to India and China.

In response to a Western embargo on seaborne Russian oil imports, Russia has been working to reroute supplies away from its traditional European markets to Asia, Africa, Latin America and the Middle East.

Russia's Foreign Minister Sergei Lavrov, who was in Nairobi on Monday hoping to nail down a trade pact with Kenya, has repeatedly travelled to Africa during the war and St Petersburg is due to host a Russia-Africa summit this summer.

In a sign of how Ukraine is trying to challenge Russia's diplomatic sway, Ukraine's Foreign Minister Dmytro Kuleba embarked on his second wartime tour of Africa last week.

Ukraine's Zhovkva said winning backing in the Global South was a top priority. While Ukraine focused on ties with Western partners at the invasion's start, securing peace was a matter of concern for all countries, he said.

He played down the prospects of calls for dialogue with Russia made by Pope Francis who described Ukraine's occupied territories as a "political problem".

"In this period of open war, we don't need any mediators. It's too late for mediation," he said.