EU and U.S. economic sanctions on Russia had a much bigger impact than previously thought, Ukraine's intelligence agency head says.

"One of the estimates which we managed to learn, Russian internal estimates, is that Western sanctions ... forced the Russian budget to lose $173bn [€151bn] already, which is quite a lot," Yehor Bozhok, the head of Ukraine's foreign intelligence service, the SZRU, told EUobserver.

The figure covered the period from mid-2014 to the end of 2018, he added.

Видео дня

The EU and U.S. imposed sanctions on Russian banks, energy firms, and arms companies after Russia invaded Ukraine and annexed Crimea. They are due to expire on 31 July unless EU states renew them by consensus.

Russia denies being at war in Ukraine and has previously said that the sanctions had no effect on its economy. The Russian embassy to the EU declined to comment on Bozhok's number.

If true, it would be more than half of Russia's state budget for 2019. It is much larger than estimates based on open sources by leading EU and US think tanks, which say Western sanctions might have been to blame for between 0.5 percent to 10 percent of Russia's economic contraction in 2014 and 2015.

Read alsoCalling on Ukraine to compromise with Russian invader "strategically foolish" – media

The SZRU figure sounded "incredibly big", an EU diplomat said.

Bozhok also cited other Russian data he said his spies had obtained.

"Just for 2019, to intervene in the Ukrainian elections, Russian special services received a top-up of $350 million," he said.

Ukraine is to hold presidential elections on March 31 and Russia was spending the money on bribing politicians, funding subversive groups, and propaganda designed to harm pro-Western candidates, he added.

Russia is also channeling funds to anti-EU radicals in Europe to meddle in the European Parliament elections in May and to aggravate divisions in the long term, Bozhok said.

Read alsoEU steps up pressure on Russia over Ukraine – media

"It's in the scale of hundreds of millions of euros a year," he told EUobserver.

"This is one of our tasks - we try to trace subversive Russian activity in Ukraine and in Europe," he said.

"I'm trying to be helpful, because European unity is in our interest - if the EU loses, we lose," he added.

Russia is also keeping 48,000 Russian soldiers on Ukraine's eastern border in a state of high readiness, Bozhok added.

"By imposing sanctions, the West is not only supporting Ukraine, it is hedging the risk that Russia will use the same money for asymmetric operations against EU countries," he said.

"How do you stop Russia? By ensuring the Kremlin's resources for foreign operations are depleted," he added.

Lieutenant general Serhiy Nayev, the commander of Ukrainian forces in east Ukraine, echoed the spy chief.

"The intensity of Russian aggression in east Ukraine was reduced because of European sanctions," he told EUobserver in a recent interview in Kramatorsk, near the front line.

He said that if Russia won in Ukraine, it would be more likely to attack other European countries, such as Poland or the Baltic states, in future.