Russian foreign ministry officials say up to 30 U.S. diplomats may be expelled from the country if the Trump administration doesn’t return two compounds seized last year by the Obama administration.

Thomas Shannon, the U.S. undersecretary of state, and Sergey Ryabkov, the Russian deputy prime minister, are expected next week to discuss the compounds in New York and Maryland.

“If the compromise is not found there, we will have to take such measures,” a Russian Foreign Ministry official told Izvestiya, the Russian newspaper, and reported more broadly by state-run media.

Russian officials had hoped there would be a breakthrough on the issue last week when President Trump met with Vladimir Putin, his Russian counterpart, on the sidelines of the G20 summit meeting in Hamburg, Germany. But though there was momentum on issues such as a ceasefire in the Syrian civil war, the issue of the compounds remained unresolved.

President Obama ordered the compounds seized and expelled 35 diplomats last December in response to Russia’s interference in the 2016 U.S. presidential election. Although Putin and Moscow have denied any interference, U.S. intelligence agencies agree that Russia tried to interfere in the election on behalf of Trump against his rival, Hillary Clinton; they say, however, there’s no evidence to indicate that interference was successful. Still, the steady stream of leaks to the media have embroiled figures close to Trump, most recently Donald Trump Jr., the president’s son. The New York Times reported that not only did Trump Jr. meet with a Russian lawyer who said she had damaging information about Clinton, but that he was told in an email that the material “was part of a Russian government effort to aid his father’s candidacy.” Trump Jr. has acknowledged the meeting, but on Monday his lawyer described the reports as “much ado about nothing.”

Amid this storm, the return of two diplomatic compounds might seem like a sideshow, but Moscow views their seizure as an affront. As I wrote at the time:

The closure of the compound in Maryland, though, represents the end of a more than four-decade Russian presence in the area. The former Soviet Union purchased the 45-acre property in Centreville, Maryland, in 1972 as a resort for Soviets living in the U.S. The compound in New York hasn’t been identified publicly, but the Russians have such a compound in Riverdale in the Bronx, which opened as a diplomatic residence in 1974. Obama said both compounds were being used for intelligence-related purposes.

Izvestia has previously reported that Russia was considering seizing the U.S. Embassy house in Moscow, as well as a U.S. warehouse in the city if the issue were not resolved.