The United States and Russia are resurrecting high-level talks aimed at resolving major irritants between the two world powers, the U.S. said Tuesday, as Russia’s top diplomat threatened retaliation against the U.S. if one of the key issues isn’t quickly settled.

With relations at what the U.S. calls a “low point,” earlier this year the two countries set up an ongoing dialogue between Undersecretary of State Tom Shannon and Russian Deputy Foreign Minister Sergei Ryabkov. The goal was to pave the way for future cooperation on Syria and other global issues by first building trust through discussions about smaller issues — including a pair of shuttered Russian compounds in the U.S. that the Kremlin wants back.

Russia abruptly canceled the last scheduled meeting between Shannon and Ryabkov in response to new Ukraine-related sanctions the Trump administration announced last month, in another sign of the deteriorating relationship between the former Cold War foes. But State Department spokeswoman Heather Nauert said Tuesday that the talks are back on track.

“Shannon has been hard at work as we have been trying to find areas that we could deal with some of these so-called irritants,” Nauert said. “And that meeting is set to happen here in Washington on Monday.”

The talks will occur less than two weeks after President Donald Trump and Russian President Vladimir Putin held a highly anticipated first meeting in Germany, an encounter both countries described as a positive first step toward improving relations. Ryabkov, speaking in Tehran to Russian media Tuesday, said the presidential meeting had inspired a “certain hope that the situation will change for the better.”

Driving the agenda for the meeting is a set of grievances both countries want the other to address, including U.S. calls for Moscow to stop harassing American diplomats and to lift a ban on U.S. adoptions of Russian children. The Kremlin is keenly focused on getting the U.S. to return control of two Cold War-era recreational estates — one in Maryland, one in New York — that former President Barack Obama seized in December as part of his response to Moscow’s meddling in the 2016 presidential election.

Though Putin declined to retaliate in December for Obama’s response — which also included expelling 35 Russian diplomats the U.S. said were really spies — frustration has mounted in Moscow amid disappointment that Trump has not reversed those actions. On Tuesday, Russian Foreign Minister Sergey Lavrov threatened unspecified retribution if the compounds, also known as dachas, aren’t given back soon.

“If this is not the case, if Washington decides not to solve this issue, we will have to take counter actions,” Lavrov said. He declined to elaborate, but Russian officials have previously floated the prospect of kicking out about 30 U.S. diplomats and seizing American government property.

The revived Shannon-Ryabkov channel was announced the same day that the president’s eldest son, Donald Trump Jr., released emails showing he’d been promised damaging information about Hillary Clinton if he met with a Moscow lawyer who was described to him as a Russian government attorney. The emails added further fuel to allegations that Trump’s campaign may have colluded with the Russian government’s efforts to help Trump win the election, though the White House and Trump Jr. have insisted that’s not the case.