Defense Secretary James Mattis has revealed that the Russian government attempted to interfere in the US midterm elections last month.

'He tried again to muck around in our elections this last month,' Mattis said of Russian President Vladimir Putin.

'We are seeing a continued effort around those lines.'

Mattis also said there is 'no doubt' that the relationship between Putin and President Donald Trump's administration 'has worsened'.

Defense Secretary James Mattis (pictured on Saturday at the Reagan National Defense Forum in Simi Valley) has revealed that the Russian government attempted to interfere in the US midterm elections last month

'We're dealing with someone we simply cannot trust,' Mattis said while speaking at the Reagan National Defense Forum in Simi Valley, California on Saturday.

And Mattis wasn't afraid to get a jab in at the Russian president as he continued to speak on the topic.

'This is a very complex situation because clearly Mr Putin a slow learner,' he told the crowd.

'He is not recognizing that what he is doing is actually creating the animosity against his people.'

Mattis wasn't afraid to take a hard line against Putin, who he claimed has 'continued efforts to try to subvert democratic processes that must be defended'.

'We'll do whatever is necessary to defend them,' he added.

Data from the midterm elections is currently being reviewed by the US intelligence community.

Mattis also said there is 'no doubt' that the relationship between Putin and President Donald Trump's administration 'has worsened'. They are pictured here together at the G20 on Friday

A report on the probe, which is searching for any evidence of foreign interference, is due later this month.

The US intelligence community previously - and unanimously - concluded that Russia interfered with the 2016 presidential election.

Mattis' revelation comes just days after Trump canceled a meeting with Putin at the G20 summit in Buenos Aires, Argentina this week.

Trump claimed the reason was Russia's aggression toward Ukraine on the border of Crimea.

'Frankly, in light of what happened with Ukraine with the ships and the sailors, it just wouldn't be the right time,' Trump told Voice of America.

The US intelligence community is currently probing whether there was foreign interference in November's midterm elections

Meanwhile, Russian officials claimed Trump had canceled the meeting due to the president's own troubles at home after his former personal lawyer, Michael Cohen, pleaded guilty to lying to Congress about Trump's business deals in Russia.

The White House then doubled down after the Kremlin reported that Trump and Putin would still speak at some point in an informal and unscheduled setting.

But on Saturday it was revealed Trump and Putin did have an 'informal conversation' during dinner at the summit on Friday night.

Putin revealed Trump had asked him what happened with the Ukrainian ships.

'I answered his questions about the incident in the Black Sea. He has his position. I have my own. We stayed in our own positions,' Putin told reporters at the G20.

'I hope that this meeting will be held eventually, when the US side is ready for it.'