Vladimir Putin has mocked the US special counsel Robert Mueller’s investigation into Donald Trump, saying “a mountain gave birth to a mouse” and the inquiry’s findings validated the Kremlin’s continuous denials of collusion with Trump’s presidential campaign.

In his first comments since Mueller presented his report to the US attorney general last month, Putin said US Democrats’ claims of a campaign conspiracy reflected their failure to accept the outcome of the 2016 election.

“It was clear for us from the start that it would end like this,” the Russian leader said of the Trump-Russia investigation. “A mountain gave birth to a mouse.”

The US attorney general, William Barr, wrote in a summary of Mueller’s still-confidential report that the special counsel found no evidence the Trump campaign “conspired or coordinated” with the Russian government to influence the election.

However, Mueller’s long investigation uncovered a multi-pronged operation to interfere with the 2016 vote and indicted 25 Russians on charges of hacking Democratic email accounts and spreading disinformation on social media.

On Tuesday Putin repeated Moscow’s across-the-board disavowals, including that the Russian government had no contact with Trump when he visited Moscow as a businessman.

“We have been saying from the start that this notorious commission led by Mr Mueller won’t find anything, because no one knows better than us: Russia has not meddled in any US election,” Putin said at an Arctic forum in St Petersburg. “There was no collusion between Trump and Russia that Mr Mueller was looking for.”

Putin described the claims of collusion between Trump and Russia as “sheer nonsense aimed at a domestic audience and used for domestic political infighting in the United States”.

He also said political tensions in the US had not abated since Mueller finished his investigation and Trump’s foes were “searching for new pretexts” to attack the president.

“Look what is going on now. Those groups which are attacking the legitimately elected president, what are they doing?” Putin said. “They disagree with the choice of the American people and seek to reduce the results to zero. This is a crisis of a political system which we have never seen in US history.”

He cast the continued pressure on Trump as disrespectful to voters, and accused senior Democrats of putting party interests above national interests.

“I’m not defending President Trump; we have plenty of disagreements,” Putin said. “His administration has introduced numerous sanctions against Russia, something we disagree with and will never accept. We consider it counterproductive.”

He said he hoped partisan fighting in Washington eased so the US and Russia could focus on issues of mutual interest, such as nuclear arms control, fighting terrorism and climate change.

“If Russia and the United States resume a full-fledged equal dialogue on issues of interest to us and entire humankind, including arms control, we will be happy to see that,” he said.

Asked if Russia would welcome Trump’s possible re-election in 2020, Putin said Moscow would “respect the choice of the American people”.