European diplomats are working to strengthen sanctions on Russia amid concerns that a potential return of former U.S. President Donald Trump could weaken Western efforts to isolate Moscow, sources told Reuters.

EU officials and diplomats are discussing several measures to ensure European sanctions hold firm over the long term, with plans to enhance enforcement even if U.S. policy shifts.

Proposed steps include "catch-all" clauses to flag and block suspicious shipments bound for Russia, along with expanded curbs on oil shipping, according to sources familiar with the talks.

There are also discussions about changing a requirement that a freeze on Russian central bank assets, the biggest single Western sanction on Moscow, must be renewed by European capitals every six months, the sources, who spoke on the condition of anonymity due to the sensitivity of the matter, said.

A few member states are working on the idea of a "catch-all" clause applied either to battlefield goods or across a broader spectrum of banned exports, three EU diplomats said.

The clause would allow customs officials to hold up shipments if the destination seemed illogical, such as crossing Russia to reach Central Asian countries.

The preparations are being made in anticipation of a change in Washington's position should Trump be reelected.

Any softening by Washington would leave Europe in a difficult position, as it is the U.S., with sweeping powers to punish sanctions violations globally, that primarily enforces the rules.

The European Union is now trying to find its own means to bolster enforcement and reinforce its curbs on Russia.

Tom Keatinge of the Royal United Services Institute think tank said European policymakers have been preparing "autonomous European sanctions considering the possibility of a Trump presidency" but would need to bolster enforcement.

"Should a Trump presidency reverse U.S. sanctions on Russia, Europeans will need to be much more muscular in enforcement action and will no longer be able to hide behind Uncle Sam," he said.

A spokesperson for the Trump campaign said that President Joe Biden's "weak agenda has emboldened our adversaries and led to war in Ukraine," criticizing Democratic presidential candidate Kamala Harris as "dangerously liberal," without outlining Trump's position on sanctions.

European countries were caught off guard during Trump's last presidency when the U.S. reversed an international deal with Iran over its nuclear program and unilaterally reinstated sanctions, leaving Europe out on a limb.

Now, European officials fear a similar about-face on Russia could unravel Western efforts to isolate Moscow, two sources said.

Trump has strongly implied on the campaign trail that he would stop or dramatically slow military aid to Ukraine if he wins the Nov. 5 election.

He has refused to state that he wants Ukraine to win the war and has even blamed Ukrainian President Volodymyr Zelensky for helping to start the conflict.

Trump has frequently praised his own 2017-2021 administration for placing sanctions on the Nord Stream II pipeline but has not made his position on future sanctions clear, stating that he wants to negotiate a quick peace deal with Moscow.

Wider sweep

European diplomats will wait until the year’s end before discussing new restrictions in earnest ahead of Poland's takeover of the six-month rotating EU presidency.

Hungary currently holds the presidency and has delayed action on sanctions. Hungarian Prime Minister Viktor Orban sparked criticism for meeting Russian President Vladimir Putin in Moscow, portrayed by Budapest as a "peace mission."

The overhaul could also eliminate the need to regularly reaffirm a freeze on Russian central bank assets, replacing six-month intervals with one of 36 months, thereby underpinning this sanction for the long term.

Assets held by the G-7 major economies amount to about $300 billion, with most held in Europe.

Several countries are also discussing a clampdown on the "mislabelling" of products destined for Russia, seeking more precise descriptions. The Baltic states that border Russia have long complained that exporters exploit EU customs codes.

EU member states are having preliminary discussions on the shape of a 15th package of sanctions after months of standstill since Budapest took the helm on July 1.

At least 45 ships are expected to be added to the EU sanctions list as Western allies seek to strengthen the G7 Russian oil price cap, one source said. Western sanctions officials believe targeting specific tankers is the best way to impact Russian oil revenues.

Western powers are also starting to pressure the countries in which the tankers are registered, sources said.

The EU also wants to expand the use of the "No Russia clause" in the next round of sanctions.

That would oblige subsidiaries of EU companies in third countries to prohibit the re-export of certain goods to Russia, including those with dual-use for military purposes, as well as ammunition and firearms.

Several countries and the European Commission aim to further restrict Europe’s other energy imports from Russia, including liquid natural gas (LNG), which have increased in recent months.

Belgium, France, and others have asked the Commission to propose ways to increase tracking of Russian LNG to the bloc.