US to make cyber capabilities available to NATO: Mattis

The United States will make its cyber warfare capabilities available to NATO, Defence Secretary James Mattis said Thursday, as allies denounced an alleged Russian bid to hack the international chemical weapons watchdog.

Mattis said the attempted attack on the Organisation for Prohibition of Chemical Weapons (OPCW) showed how cyber attacks were becoming "more frequent, more complex and... more destructive".

"This is why the United States, like the United Kingdom, Denmark, the Netherlands, Estonia will provide national cyber contributions to help NATO fight in this important domain," Mattis told reporters at a meeting of NATO defence ministers.

The Netherlands revealed extraordinary details of the plot by Russia's GRU military intelligence agency against the OPCW in The Hague, including photos of the alleged agents and their equipment.

Mattis refused to be drawn on what kind of response the OPCW plot should be met with, saying "tit for tat on cyber" was not necessarily appropriate, but he insisted the Kremlin must face consequences.

"Basically the Russians got caught with their equipment, with their people who were doing it and they have got to pay the piper. They are going to have to be held to account," Mattis said.

"We have a wide variety among our nations of responses available to us."