The American embassy in Kiev announced Wednesday its temporary closure due to the possibility of Russia launching a “significant air attack” on the city. The move comes a day after Ukraine significantly escalated the conflict by using long-range U.S. missiles on targets within Russia.

“The U.S. Embassy in Kyiv has received specific information of a potential significant air attack on November 20,” the announcement for the temporary closure read. “Out of an abundance of caution, the Embassy will be closed, and Embassy employees are being instructed to shelter in place.”

This news comes the same day as Washington’s announcement that antipersonnel mines will be given to Ukraine. This would represent a second major escalation within the past week, particularly as Ukraine is technically a signatory to the Ottawa treaty, which bans antipersonnel mines.

Humanitarian groups have condemned the decision of the Biden administration. “Antipersonnel landmines are inherently indiscriminate weapons that maim and kill civilians long after conflicts end and shouldn’t have a place in the arsenal of any country,” Ben Linden, Amnesty International’s Advocacy Director for Europe and Central Asia, stated. “Even the 'nonpersistent' mines are a threat to civilians.”