Russia's Foreign Minister Sergey Lavrov has dismissed allegations that Moscow meddled in the US presidential election that brought Donald Trump to the White House as "blather".

His comments on Saturday came a day after authorities in the United States indicted 13 Russian nationals and companies with running a huge secret campaign against Trump's 2016 rival, Hillary Clinton.

"You can publish anything, and we have seen those indictments multiplying, the statements multiplying," Lavrov said on Saturday at a major security conference in the German city of Munich.

"As long as we don't see facts, everything else is blather."

Major investigation

The indictments detailed a multimillion-dollar operation launched in 2014 to interfere with "the US political and electoral processes, including the presidential election of 2016".

The charges brought by US Special Counsel Robert Mueller allege that by mid-2016, the campaign - under the direction of Yevgeny Prigozhin, a close ally of Russian President Vladimir Putin - became focused on boosting Trump and demeaning his rivals, including Clinton.

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The operation allegedly involved hundreds of people working in shifts.

A major target of the probe is the St Petersburg-based ''Internet Research Agency", also known as "The Troll Factory".

It is accused of manipulating social media in the US and staging political rallies in support of Trump

According to the indictment, Russian impostors on social media used hashtags such as "TrumpTrain", "Trump2016", "Hillary4Prison" and "MAGA", a reference to Trump's slogan "Make American Great Again".

However, the indictments made no judgement on whether the alleged Russian campaign had affected the outcome of the election.

In his comments to the Munich Security Conference, Lavrov said that US officials, including Vice President Mike Pence, had in the past "denied that any country influenced results of the election".

'Incontrovertible'

But speaking at the same event, US National Security Adviser HR McMaster said the evidence that Russia tried to meddle with the US election was undeniable.

"We're becoming more and more adept at tracing the origins of this espionage and subversion, and as you can see with the FBI indictment, the evidence is now really incontrovertible and in the public domain," McMaster said.

"Now, this is in the arena of a law enforcement investigation, it's going to be apparent to anyone."

In his speech, McMaster also spoke about the alleged use of chemical weapons by the government of Syrian President Bashar al-Assad, saying the US would use military force if such attacks continued.

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"Public accounts and photos clearly show that Assad's chemical weapons use is continuing," said McMaster, a serving army general.

"It is time for all nations to hold the Syrian regime and its sponsors accountable for their actions."

In April 2017, the US fired several missiles at a Syrian airbase in retaliation for an alleged chemical attack on Khan Sheikhoun that killed scores of people.

Since then, the Syrian government has been accused several times of using chemical weapons against its citizens, most recently in the rebel-held territory of Eastern Ghouta.

Those allegations have been denied by the Syrian government.

Eastern Ghouta is the last remaining rebel stronghold near the capital, Damascus, and has been under a government siege since 2013.

It is believed that around 400,000 people still live in the area, which suffers from acute food and medicine shortages.