Russian President Vladimir Putin and US President Donald Trump will have a detailed discussion about the Syrian conflict when they meet at their first official summit in July, the Kremlin says.

The meeting, to be held on July 16 in Helsinki, is likely to worry some US allies, particularly those who want to isolate Russia on the international stage, as well as drawing a fiery reaction from some of Trump's critics at home.

Russia's support for Syrian President Bashar al-Assad, whom the US and its Western allies accuse of using chemical weapons against civilians, has been one of the main flashpoints in the tense relationship between Washington and the Kremlin.

"There's no doubt about the fact that Syria will be discussed in depth," Kremlin spokesman Peskov said in a call with reporters on Friday. "A thoroughly exhaustive discussion awaits."

Other contentious issues are also likely to come up in the meeting, which will mark the third time the two presidents meet but their first official summit.

Trump could raise the issue of Russia's alleged meddling in the US elections in 2016, a claim made by US intelligence agencies that led the United States to impose tough sanctions on Russia in April.

Previously, sanctions had been imposed during the administration of President Barack Obama in response to Russia's annexation of Crimea and its involvement in the conflict in Ukraine.

"If (the issue of election meddling) will be raised by the US president, then the Russian president will repeat that Russia could not and did not have anything to do with this situation, around which such insinuations are unfurled," Peskov said.

Peskov also said Putin was ready to move towards normalising ties with the United States in proportion to US willingness to do the same.

Trump will meet Putin in Helsinki after attending a July 11-12 summit of NATO leaders and a visit to Britain. The date will give Putin a chance to attend the July 15 closing ceremony of the soccer World Cup hosted by Russia.

After Trump and Putin met briefly in Vietnam in November 2017, Trump was criticised in the US for saying he believed Putin when the Russian president denied Russian meddling.

The upcoming Helsinki summit has been criticised by members of the opposing Democratic Party who described it as a gift to the Kremlin and expressed concerns over what else Trump might give away.

In Moscow, Russian Foreign Ministry spokeswoman Maria Zakharova said it was best not to get too excited about what the summit might yield.

"In general, I'd recommend everyone not to use phrases like 'breakthroughs' and such like," the RIA news agency quoted her as saying.

"I suggest taking quite a pragmatic and realistic view of these meetings."