Deputy Foreign Minister Sergei Ryabkov said in a statement to Russian news agencies that Moscow had many claims against the behavior of US diplomats in Moscow but had preferred not to bring them into the public sphere.

"We categorically reject the charges against the staff of Russian diplomatic institutions in the United States," he was quoted as saying by the ITAR-TASS news agency, saying it was "illegal" for diplomats to have been watched by the authorities in this way.

"If the American authorities have claims against our citizens... they should have been made first through diplomatic channels.

This is no more than cheap measure and an attempt to fulfill an order by Russophobes in the US," he added.

Ryabkov hinted that Russia had many allegations it could lay against American diplomatic staff if it so desired but said Moscow had preferred stay quiet.

"We have many claims against how American embassy staff work and act. But we do not want to go down the path of a rhetorical war of mutual accusations," he said.

The scandal risks causing a new crisis in US-Russia relations which have already been scarred by Russia's decision to grant asylum to US intelligence leaker Edward Snowden and a host of other issues including human rights.

There had been signs in the last weeks of a better atmosphere, particularly after Washington and Moscow worked together on a deal to rid Syria of its chemical weapons and have attempted to realize a plan for a peace conference on the Syrian conflict.

Ryabkov said the case had been created by those in the United States who wanted to spoil constructive trends in US-Russia relations.

"Someone in Washington needed to spoil the atmosphere -- we cannot see this any other way."

Russian senator Ruslan Gattarov described the charges as "petty revenge on the part of the hawks in the State Department."

NJF/NJF