WASHINGTON (BLOOMBERG) - Russian Foreign Minister Sergei Lavrov said that the US arrest of Russian Maria Butina on suspicion of trying to infiltrate Republican circles and acting as an unregistered foreign agent was unacceptable.

In a telephone conversation with US Secretary of State Michael Pompeo, the top Russian diplomat said the charges against Butina were fabricated and called for her prompt release, according to a Foreign Ministry statement.

Butina was ordered jailed in the US on July 19 until her trial on charges she conspired to establish a back channel between Russians and American politicians.

She faces an additional charge of operating in the US as an unregistered agent of Russia.

Prosecutors said she had ties to Russia's intelligence services and oligarchs who could offer her safe harbour.

She pleaded not guilty.

Among other issues, Lavrov and Pompeo also discussed possible cooperation between Russia, the US and other countries in solving Syria's humanitarian crisis.

They also talked about efforts to denuclearise the Korean peninsula.