(AP) — In an escalating tit-for-tat, the United States forced Russia on Thursday to shutter its consulate in San Francisco and scale back its diplomatic presence in Washington and New York, as relations between the two former Cold War foes continued to unravel.

The Trump administration said the move constituted its response to the Kremlin’s “unwarranted and detrimental” decision to force the U.S. to cut its diplomatic staff in Russia. The U.S. gave Russia a mere 48 hours to close its San Francisco consulate, along with smaller Russian posts in Washington and New York.

“The United States is prepared to take further action as necessary and as warranted,” said State Department spokeswoman Heather Nauert. Still, she said the U.S. hoped both countries could now move toward “improved relations” and “increased cooperation.”

Russia said it regretted the order and pointed the finger at the U.S. for starting the “escalation of tensions” between the nuclear-armed powers.

It wasn’t immediately clear whether the Kremlin would return the volley by retaliating for the U.S. retaliation. The Russian Foreign Ministry said Moscow was studying the decision to determine its response.

U.S. ties to Russia have soured in recent years over deep disagreements about Ukraine, Syria and Russian hacking. To the surprise of those who anticipated that President Donald Trump’s election would reverse that trend, the feud has only worsened this year, even as investigators continue probing whether Trump’s campaign colluded with Moscow’s efforts to help him get elected.

In addition to its consulate, the Russians by Saturday must close an official residence in San Francisco. Though Russia can keep its New York consulate and Washington embassy, Russian trade missions housed in satellite offices in those two cities must shut down, said a senior Trump administration official. The official briefed reporters on a conference call on condition of anonymity.

The U.S. isn’t expelling any Russian officials, so those who work at the shuttered offices can be reassigned elsewhere in the U.S., the official said.

One of the buildings is believed to be leased, but Russia will maintain ownership over the others, the official said, adding that it would be up to Moscow to determine whether to sell them or otherwise dispose of them.

The forced closures were the latest in an intensifying exchange of diplomatic broadsides with origins in Washington’s opposition to Russia’s actions in Ukraine and its interference in the 2016 presidential election.

In December, former President Barack Obama kicked out dozens of Russian officials in the U.S., shuttered Russian recreational compounds in New York and Maryland, and sanctioned Russian individuals and entities.

Russian President Vladimir Putin held off on any retaliation, and the next month, Trump took office, having campaigned on hopes of improving U.S.-Russia ties.

But earlier this month, Trump begrudgingly signed into law stepped-up sanctions on Russia that Congress passed in an attempt to prevent Trump from easing up on Moscow. The Kremlin quickly retaliated, announcing the U.S. must cut its own embassy and consulate staff down to 455.

Although Russia said 755 personnel would have to go to reach that number, Washington never confirmed how many diplomatic staff it had in Russia at the time. As of Thursday, the U.S. has complied with the order to reduce to 455, officials said.

That reduction also led the U.S. to temporarily suspend processing non-immigrant visas for Russians seeking to visit the U.S. Visa processing will resume soon, but at a “much-reduced rate” owing to fewer staff to process the visas, the official said. Earlier, the U.S. had said it would start processing visas only at the embassy in Moscow, meaning Russians could no longer apply for visas at the U.S. consulates in St. Petersburg, Yekaterinburg and Vladivostok.

Despite the exchange of penalties, there have been narrow signs of cooperation between the two countries that has transcended the worsening ties. In July, Trump and Putin signed off on a three-way deal with Jordan for a cease-fire in southwest Syria that the U.S. says has largely held intact.

Secretary of State Rex Tillerson conveyed the decision to shutter the Russian posts to Russian Foreign Minister Sergey Lavrov in a Thursday phone call in which he also told Lavrov that the U.S. had complied with Moscow’s order to cut its diplomatic staff. Lower-level officials also spoke to their Russian counterparts in the U.S. about the details of the new U.S. order.

Given the reciprocal nature of the escalating tensions over the past year, it was likely the Kremlin would feel compelled to respond by taking further action against Washington. Nevertheless, the United States argued that the score has been evened.

U.S. officials pointed out that Russia, when it ordered the cut in U.S. diplomats, had argued it was merely bringing the size of the two countries’ diplomatic presences into “parity.” Both countries now maintain three consulates on each other’s territory and ostensibly have similar numbers of diplomats posted, though such numbers are difficult to independently verify.

“The United States hopes that, having moved toward the Russian Federation’s desire for parity, we can avoid further retaliatory actions by both sides,” Nauert said.