The Kremlin said ahead of the meeting that the leaders would discuss bilateral ties as well as "security issues on the European continent and regional conflicts," an allusion to the standoff between Russia and the West over Ukraine.

Orban has said he will seek an agreement to increase Hungary's gas imports from Russia at a time when some in Europe accuse Russia of orchestrating an energy crisis to pressure European countries.

Hungary's opposition parties released a joint statement calling on Orban to cancel his trip, describing it as "contrary" to national interests.

The opposition said that, by meeting with Putin, Orban "indirectly encourages the Russian president to further escalate the current tense situation."

US President Joe Biden has accused Russia of plans to invade Ukraine imminently with its troops massed on the border and warned of severe economic sanctions if it does.

Orban's visit is also likely to sit uncomfortably with Hungary's closest European Union allies, most notably Poland.

Warsaw has presented a united front with Budapest against Brussels on issues like the rule of law, but resents Orban's ties with Putin.

Polish Prime Minister Mateusz Morawiecki visited Kyiv Tuesday for talks with Ukrainian President Volodymyr Zelensky, who is backed by the West.

- 'Peace and de-escalation' -

At a meeting of European conservatives organised by the Spanish far-right in Madrid over the weekend and also attended by Morawiecki, Orban said that Ukraine was a "very important issue" for those in Central Europe.

He stressed he was in favour of "peace and de-escalation," according to his office.

But he did not echo the general EU alarm over Russia's troop buildup on Ukraine's border.

Hungary, which joined NATO in 1999 and the EU in 2004, has taken a softer line on Ukraine, with which it shares a small land border.

Hungarian Defence Minister Tibor Benko said in an interview Tuesday morning that leaders should shy away from "Cold War rhetoric".

"There's no need for 1,000 NATO soldiers to come to Hungary and be stationed here permanently," he told public media, adding "no one wants to create a situation where people are afraid and worried by showing off their forces".

Biden has announced plans to send US troops to NATO countries in eastern Europe, though not to Ukraine itself, which is not a member of the transatlantic Alliance.

Orban is popular at home despite critics' accusations of rampant corruption and that he is steering Hungary towards authoritarianism.

The Moscow visit comes just two months before the critical election in Hungary, with polls indicating a close race between Orban and a united opposition alliance.

Under Orban, who began his political career in Hungary's anti-Soviet democracy movement, Budapest has been one of Russia's closest EU partners.

In a sign of friendship, Hungary was the first bloc member to approve Moscow's Sputnik V coronavirus vaccine, which has not been green-lighted by the European Medicines Agency (EMA).