Russian President Vladimir Putin talks on the sidelines of the 20th St. Petersburg International Economic Forum in St. Petersburg, Russia, 17 June 2016. EPA/SERGEY CHIRIKOV

President Vladimir Putin said on Friday he accepted the United States was probably still the world's sole superpower and he was ready to work with whoever won the presidency, but didn't want to be told how to live by Americans.

Putin's comments follow a rocky period in US-Russia relations, which have been undermined by disagreements over issues such as Ukraine and Syria.

Putin reiterated criticism of what he said was the misguided role of the United States in Ukraine's affairs and said he opposed what he cast as US efforts to prevent Russia repairing its relations with the European Union.

But he had some positive words too.

"America is a great power — today probably the only superpower. We accept that," Putin said at the St. Petersburg International Economic Forum. "We want to and are ready to work with the United States."

Asked about Donald Trump, Putin appeared to play down positive comments he had made about the Republican contender in the past, saying those had been misinterpreted.

In December, Putin described Trump as "very flamboyant," "very talented," and "an absolute leader in the presidential race."

Those comments, along with warm words from Trump about Putin, have fueled speculation the Kremlin would be pleased to see Trump in the White House.

But on Friday Putin said he had only described Trump as "flamboyant."

"He is, isn't he?" said Putin with a smile. "I did not give any other assessment of him."

Putin said he welcomed Trump's desire to restore US-Russia ties. "What's wrong with that?" Putin asked, drawing applause from the audience.

He appeared keen however to hedge Russia's bets by avoiding the impression he was taking sides, and also emphasized his "warm relations" with former US President Bill Clinton, whose wife Hillary is running for the White House.

Putin said he was grateful for the attention and respect Bill Clinton had shown to Russia and Putin personally.

He had less to say about Hillary Clinton though, saying he had never worked with her directly.

Putin added that Russia did not hold a grudge against the European Union and was ready to improve relations, but he offered little prospect that mutual sanctions would be eased soon.

Speaking on the day the EU said it would extend sanctions on Russia imposed over its annexation of Crimea in 2014, Putin played down their impact and painted a bullish picture of an economy recovering despite low oil prices.

But in a disappointment for investors, he provided little hope that either Russia or the EU were likely to soften their sanctions, and was vague about the steps Russia would take to improve its investment climate.

"We do not hold a grudge and are ready to meet our European partners halfway," Putin told the annual St Petersburg International Economic Forum. "But it certainly cannot be a one-way game."

Despite lingering tensions over Ukraine, there are tentative signs of a thaw in relations and European Commission President Jean-Claude Juncker met Putin at the St. Petersburg forum.

They did not discuss the sanctions, however, Kremlin spokesman Dmitry Peskov said, according to the Tass news agency.

Replying to investors' questions, Putin said Russia did not intend to soften its counter-sanctions, banning most European food imports, before the EU's sanctions were lifted.

He blamed the United States for persuading European countries to continue sanctions against their own interests.

"They (Russian counter-sanctions) affect Europe, but they don't affect the US — they have nil effect," Putin said. "But the US says to its partners: 'you need to put up with it'. Well, if they want to, let them put up with it.

Putin said Russia was liberalising its investment climate, but offered few specifics, except to pledge that he would sack governors who failed to support business.

Russia had weathered economic difficulties successfully, he said, citing falling inflation and capital flight and the preservation of foreign exchange reserves.