(Reuters) -Improving relations between Russia and the United States will take time, Kremlin’s spokesman Dmitry Peskov told the Russian TASS state news agency in remarks published on Wednesday.

“There is, of course, inertia in this process,” Peskov told TASS, referring to the prolonged absence of a meeting between Russia’s President Vladimir Putin and U.S. President Donald Trump.

“It takes time for efforts to bring bilateral relations back onto a normal track.”

TASS reported that for the first time in modern Russian history more than six months have passed since a new U.S. president’s inauguration without a summit with the Russian leader.

U.S. special envoy Steve Witkoff is expected in Moscow on Wednesday to meet with Russian leadership in yet another diplomatic effort by Washington to bring the war in Ukraine to an end.

Russia-U.S. ties have been marked by escalating tensions in recent weeks, with Trump saying he had ordered two nuclear submarines to be positioned in “the appropriate regions” in response to remarks by former Russian president Dmitry Medvedev.

Trump has also issued an ultimatum to Putin, demanding a ceasefire in the war that Russia started, with a full-scale invasion on Ukraine in February 2022, and a formal peace agreement by Aug. 8.

Trump threatened to hit Russia with new sanctions and impose 100% tariffs on countries that buy its oil – of which the biggest are China and India – unless Putin agrees to a ceasefire in the war.

(Reporting by Lidia Kelly in Melbourne; Editing by Himani Sarkar and Michael Perry)