US President Barack Obama said on Tuesday if Russia had engaged in hacking Democratic Party organizations it would be an issue he would discuss with President Vladimir Putin, but it would not "wildly" alter the countries' relationship.

The United States already has "a lot of differences with Russia on a whole bunch of issues, but I think that we've been able to try to stay focused on those areas where we still have a common interest," Obama said at a news conference during a state visit with Singapore's Prime Minister Lee Hsien Loong.

Calling the relationship between the United States and Russia tough and difficult, Obama noted common concerns.

"Potentially we have an interest in bringing an end to violence in Syria," Obama said. "How do we balance those issues? That's pretty standard state craft at this point with Russia."

However, blaming Putin's intelligence services on any hacks would pressure Obama's administration to divulge its evidence, which relies on classified sources and methods, US intelligence officials said on Monday.

"If in fact Russia engaged in this activity, it's just one on a long list of issues that me and Mr Putin talk about and that I've got a real problem with," Obama said.

The US has provisions in place so if it sees evidence of a malicious cyber attack by a state actor it can impose penalties.

"But that requires us to really be able to pin down and know what we're talking about," Obama said, adding he did not want to get ahead of any of the legal evidence and facts.

Russia has denied responsibility for hacking the emails of the Democratic National Committee. A computer network used by Democratic presidential nominee Hillary Clinton's campaign, and the party's fundraising committee for the US House of Representatives were also hacked.

The US Department of Justice national security division is investigating whether the cyberattacks threatened US security.

Debbie Wasserman Schultz, the chairwoman of the DNC, resigned in the wake of the release of thousands of hacked emails. Some of the emails appeared to show favoritism within the DNC for Clinton over US Senator Bernie Sanders of Vermont.