The US government determined on Tuesday that the events in Myanmar constitute a coup and thereby warrant a cut in US aid to the military government.
The State Department decision is the first major foreign policy declaration by the team on Asia since President Joe Biden took office on January 20.
"After a careful review of the facts and circumstances, we have assessed that Aung San Suu Kyi, the leader of Burma's ruling party, and Win Mynt, the duly elected head of government, were deposed in a military coup on February 1," a senior official said.
Both leaders have been detained.
"A very small circle of Burma's military leaders have chosen their own interests over the will and well-being of the people," the official said.
The decision was made after a review of the events, in which the country's military took power after claiming the November election was fraudulent.
It means an immediate cut to US assistance to the government but not to civil society groups in the country, or to the Rohingya refugees and other people in need.
The US is also reviewing the possibility of imposing sanctions on those responsible for the coup.
“We will take action against those responsible, including through a careful review of our current sanctions posture as it relates to Burma's military leaders and companies associated with them."
Myanmar’s army chief, Min Aung Hlaing, who is now in charge after the military seized power, has already been subjected to sanctions and a visa ban by the US.
Gen Mark Milley, the chairman of the Joint Chiefs of Staff, has been trying to reach Mr Hlaing, but his attempts have failed so far, Politico reported on Tuesday.
Republican Senate leader Mitch McConnell said he had spoken to Mr Biden and Secretary of State Antony Blinken about the situation in Myanmar.
Mr McConnell also classified the events as a coup and called for swift sanctions by the US.
But it is unclear how much influence the US holds by cutting foreign assistance to the government, as it makes up only a small portion of US aid to Myanmar.
Officials said there had not yet been any contact between the Biden administration and the military leaders, and that for now, the US was co-ordinating with regional allies such as Japan and India.
By calling the events a coup, the Biden administration is taking a symbolic pro-democracy stance in its policy towards the region.
This pits it against China’s position. China shares a long border with Myanmar, has strong relations with the military and has refrained from calling it a coup.
Chinese Foreign Ministry spokesman Wang Wenbin urged the country’s leaders to “properly handle their differences" and "maintain political and social stability".
The US removed some of its sanctions on Myanmar after the 2010 elections that began the country’s transition to a more democratic system.
But in 2017, as a military crackdown began and as the Rohingya refugee crisis intensified, some of the sanctions were reimposed.