The European Union's sanctions, painfully negotiated by all 28 EU governments in 2014 and so far renewed every six months, are the bloc's toughest response to Russia's annexation of Crimea and its support for separatists in eastern Ukraine.

But it is up to each EU government to enforce them and they do not apply to companies' Russian subsidiaries, making any possible wrongdoing very hard to prove.

Reuters reported on July 5 that two electricity turbines made by Siemens were shipped to the Black Sea peninsula of Crimea, which is subject to EU sanctions that ban EU firms from supplying energy technology there. Siemens said the turbines were transferred to Crimea without its knowledge and against its will.

"Implementation and enforcement of EU restrictive measures rests with the member states," a spokesman for the European Commission said in response to the Siemens case. "The Commission is in touch with the German competent authorities on this particular case," the spokesman said, referring to Siemens.

Still, economic sanctions on Russia, including those on Crimea, have deterred many EU firms from doing business there.

EU exports to Russia fell by 40 percent between 2013 and 2016 to 72 billion euros ($82.09 billion), according to the EU's statistics office Eurostat. Direct investment by the European Union's 28 countries into Russia fell 18 percent to 162 billion euros between 2013 and 2015, the latest data available.

"The reputational damage of a potential sanctions breach can be enormous," said Maya Lester, a London-based barrister and author of a European sanctions website. "One practical effect of imposing sanctions can be about sending a message, as well as the restrictions themselves, and compliance is a big issue too."

Overall, the European Union has imposed sanctions banning most EU business with Crimea, has frozen the assets and prohibited travel for Russians linked to the Ukraine crisis and has limited EU investment in Russia's defence and energy sectors. Financing to Russian banks is severely restricted.

Unlike the United States, which has robust economic and trade sanctions enforcement through its Office of Foreign Assets Control at the U.S. Department of the Treasury, the European Union has no single such agency.

While the EU's institutions in Brussels are instrumental in drawing up the legal language for the punitive regime and drumming up diplomatic support for them, the few dozen experts who help design them do not have the resources to enforce them.

"Theatrical rhetoric is not matched by enforcement," said Tom Keatinge, director of financial crime studies at RUSI think-tank in London. "They have become symbolic," he said, saying not enough was done to update sanctions to avoid both EU and Russian companies circumventing them.

A Sept. 2016 investigation by Reuters showed that at least two European retailers, Auchan and Metro, were active on the Crimean market through Russian subsidiaries, shipping there from Russia via a ferry and port that are subject to EU sanctions.

Furthermore, France last year granted Russian Agriculture Minister Alexander Tkachev a visa even though he has been banned from entering the EU since 2014 because of Crimea.

NO DATABASE

In April, Britain moved to a U.S.-style enforcement policy to allow civil fines of at least 1 million pounds ($1.28 million) on breaches of financial sanctions.

    However, Britain has not so far prosecuted any company for any potential breach of sanctions, Lester said.

    It was not immediately clear if other EU countries have brought criminal proceedings because no public database exists of sanctions breaches.

Many EU countries rely on different agencies, from the central bank to the export licensing authority, to enforce measures. Refusal of licenses can be challenged in court, while customs offices and the public prosecutor are responsible for violations of export controls.

EU officials have designed sanctions to be as specific as possible to avoid hurting the wider population, making loopholes easier to find. EU companies are expected to adhere to what EU officials call "the spirit" of the sanctions regime but it does not apply directly to their subsidiaries incorporated in Russia.

"If the sanctions are too wide ranging, they may be too disruptive to the EU, or contribute to a financial crisis," said Erica Moret, chair of the Geneva International Sanctions Network at the Graduate Institute Geneva. "The human costs of blanket sanctions have been too great in the past."

EU governments also want the measures to be able to be lifted quickly in case of a rapprochement with Russia.

Defence, energy and financial sanctions could be removed if all sides implement the Minsk peace deal involving the withdrawal of troops and weaponry from eastern Ukraine.

Russian denies any direct involvement in the conflict that has killed more than 10,000 people since April 2014.

(Additional reporting by Alissa de Carbonnel; editing by Philippa Fletcher)

By Robin Emmott