Appearing alongside Mr Putin at a BRICS summit in the Russian city of Kazan, Antonio Guterres called on the Russian leader to agree a peace deal "in line with the UN Charter, international law and UN General Assembly resolutions".

It comes after President Xi Jinping claimed on Wednesday that China and fellow BRICS member Brazil both have peace plans for the war in Ukraine.

He told Mr Putin and other leaders at the three-day summit that they intend to rally further international support in the hope of bringing fighting there to an end.

Mr Xi said: "We must uphold the three key principles: no expansion of the battlefields, no escalation of hostilities, and no fanning flames and strive for swift de-escalation of the situation."

The BRIC coalition formed in 2009, bringing together Brazil, Russia, India, and China. South Africa joined the following year, changing the name to BRICS.

It was largely disregarded at first - but it has since grown in both membership and influence with Russia's war in Ukraine and Iran's involvement in the wars in Gaza, Israel, and Lebanon dominating global geopolitics.

Just weeks before Russia invaded Ukraine in February 2022, Mr Putin and Mr Xi signed a "no limits" partnership between their two countries.

Beijing, however, has kept largely quiet on the Ukraine war and not tried to use its influence on Moscow to bring it to an end as many had hoped. This week's claims of a peace plan could reignite those hopes.

India's Prime Minister Narendra Modi added that his country "supports dialogue and diplomacy, not war".

Mr Guterres has not visited Russia in over two years and the decision sparked criticism from Ukrainian officials.

Ukraine's foreign ministry wrote on X ahead of the summit that the trip would "only damage the UN's reputation". "This is a wrong choice that does not advance the cause of peace," it added.

Farhan Haq, deputy spokesman for Mr Guterres, responded by saying it is "standard practice in attending meetings of organizations with large numbers of important member states, such as the G7 and the G20" - pointing out that BRICS countries represent "half the world's population".

Notably, Turkey's President Tayyip Erdogan, who is hoping to enter the European Union, was also there.

Appearing alongside BRICS members on Thursday, Mr Guterres also called for peace in the conflicts in Gaza, Lebanon, and Sudan.

On the Middle East, Mr Xi called for a comprehensive ceasefire in Gaza.

Alternative payment system would counter sanctions

In a joint declaration bringing the three days to a close, BRICS members voiced concern about "the disruptive effect of unlawful unilateral coercive measures, including illegal sanctions".

Mr Putin's priority for the meeting was discussions of an alternative global payment system that could be used between members - after Russia was cut off from SWIFT at the outbreak of its invasion.

As such, the attendees' statement talked of a "faster, low-cost, more efficient, transparent, safe and inclusive cross-border payment instruments built upon the principle of minimising trade barriers and non-discriminatory access".

On the sidelines of the summit, Mr Putin also met Iranian President Masoud Pezeshkian.

He reitirated the "truly friendly" ties between Russia and Iran that he hopes will be solidified with a "comprehensive strategic partnership treaty", which is due to be signed by the pair on Mr Pezeshkian's planned trip to Moscow.

A date for that visit has not been decided, Kremlin foreign affairs adviser Yuri Ushakov said.

Commenting on the Middle East crisis, Mr Pezeshkian added: "The flames of war continue to rage in the Gaza Strip and
cities of Lebanon, and international institutions, particularly the UN Security Council as a driver of international peace and security, lack the necessary effectiveness to extinguish the fire of this crisis."