The two Russian diplomats who face expulsion from the Netherlands for spying had at least 10 sources for information, Erik Akerboom, chief of domestic security agency AIVD, told radio programme Nieuws en Co.

‘We were able to establish fairly intensive contacts in more than ten cases, and information was transferred for payment in a number of them,’ Akerboom said. The spies and their sources had been observed for some time, and the companies affected by the claims were only informed this week, Akerboom said.

The Russian embassy in The Hague told Russian news agency Tass that ‘no evidence that might prove their illegal activity in the country’s territory was presented’. ‘Retaliatory measures will follow,’ the embassy said. This is likely to mean two Dutch diplomats will have to leave Russia.

While one of the sources was foreign, and will now have to leave the country, it is unclear as yet what will happen to the rest.

It is not illegal to have contact with a foreign intelligence service but violating state, official and trade secrets is a criminal offence.

The AIVD said it does not know if the sources have breached these rules, but says this is likely, given they worked at companies and at a ‘higher education institution’ which carries out research into artificial intelligence, quantum computers, semiconductors and nanotechnology.

‘We are now trying to determine the extent of the damage,’ Akerboom told the radio programme.