The Embassy of Canada to Ukraine, located in Kyiv, has temporarily suspended in-person services after U.S. officials there warned they'd received information about a "potential significant air attack," cautioning citizens to shelter in place if they hear an air alert.

Read the bulletin.

Several hours after the U.S. shared the advisory, Ukraine's military spy agency said Russia was trying to spread misinformation with fake online messages.

"Do not ignore air raid sirens — it is safer to wait in a shelter. However, we urge you not to succumb to panic," reads a Ukrainian-language message shared to Telegram by the agency.

The agency said Russia is "spreading a message about the threat of a 'particularly massive' missile and bomb attack on Ukrainian cities today … This message is a fake."

The Spanish, Italian and Greek embassies have also shut down as a precaution.

New tensions have emerged as the war passed its 1,000-day mark on Tuesday. U.S. President Joe Biden publicly authorized Ukraine to use American-supplied longer-range missiles to strike deeper into Russia. 

The same day, Moscow said the Ukrainians fired six of them into the Bryansk region, which shares a border with Ukraine and Belarus. The military reportedly shot down five of the missiles, known as ATACMS, and damaged the sixth.

"They're not going to change the course of the war," said Fraser, referring to the missiles and the newly allowed use of American-supplied antipersonnel land mines, as announced by the Biden administration on Wednesday. 

He said the new U.S. policies give "some light into just how dour the Ukrainian situation is becoming."

While Ukrainian forces have held on to hundreds of square-kilometres of Russian territory in the Kursk region, Russia controls thousands in eastern Ukraine. North Korean troops, who are fighting with Russia, are aiding in the fight to reclaim Russian ground.

Russian President Vladimir Putin has also lowered the threshold for using his country's nuclear arsenal. potentially allowing for its use in response to a conventional attack by any nation supported by a nuclear power. Fraser predicted Russia will turn its attention to Ukrainian gas, electricity and water infrastructure "to make Ukrainians feel the cold in the wintertime."

With files from The Associated Press