WASHINGTON - The United States is ramping up COVID-19 vaccine rollout as January marks the deadliest month yet since the onset of the pandemic in the country.

In face of growing frustration over vaccine shortages, US President Joe Biden announced Tuesday a roughly 16 percent boost in vaccine deliveries to states over the next three weeks.

The country expects to provide enough doses to vaccinate 300 million Americans by the end of the summer or early fall, according to Biden.

Biden, calling the push a "wartime effort", said the administration was working to buy an additional 100 million doses of each of the two approved coronavirus vaccines from Moderna and Pfizer.

"The brutal truth is it's going to take months before we can get the majority of Americans vaccinated. Months. In the next few months, masks, not vaccines, are the best defense against COVID-19," he said.

Shortages have been so severe that some vaccination sites around the United States had to cancel tens of thousands of appointments with people seeking their first shot, according to media reports.

"We appreciate the administration stating that it will provide states with slightly higher allocations for the next few weeks, but we are going to need much more supply," said Maryland Governor Larry Hogan.

With nearly 80,000 reported deaths through Jan 26, the first month of 2021 is the deadliest month yet since the pandemic hit the United States one year ago.

The grim January toll surpassed the previous high set in December with five days remaining in the month, according to data from Johns Hopkins University.

The spread of coronavirus variants added to public fears.

The first US case of a coronavirus variant discovered in Brazil was confirmed in Minnesota earlier this week. Another strain, first discovered in Britain, has been detected in more than 20 US states, according to data of the US Centers for Disease Control and Prevention.

The threat of variants has made reopening the state a greater concern in California, a recent epicenter of the pandemic in the country, Los Angeles County Public Health Director Barbara Ferrer said.

"We do need to move through the next few weeks with caution. At many other points where we've been reopening our sectors, we in fact have seen a bump up in our cases we can't really afford that," she said.

Just weeks into California's rollout of the coronavirus vaccine, evidence is emerging of inequities in who is getting the medicine, the Los Angeles Times reported.

Los Angeles County officials said they are concerned about low vaccination numbers among healthcare workers in South Los Angeles and other communities of color.

The United States has recorded more than 25.5 million COVID-19 cases with over 427,000 related deaths as of Wednesday afternoon, according to the real-time count kept by Johns Hopkins University.