WASHINGTON — As the U.S. enters “what may well be the toughest and deadliest period of the virus,” President Joe Biden announced a national COVID-19 strategy Thursday that aims to ramp up vaccinations and testing, address inequality and increase the use of masks — including a requirement that they be worn for travel.

In his first such briefing at the White House, Biden laid out his strategy for combating the pandemic while warning Americans that things would get worse before they get better. He signed 10 executive orders to kick off his pandemic response.

“The past year, we couldn't rely on the federal government to act with the urgency and focus and coordination we needed, and we have seen the tragic cost of that failure,” Biden said.

“We didn't get into this mess overnight and it's going to take months for us to turn things clear. We will get through this.”

Biden cautioned that the death toll is likely to reach 500,000 next month, and he said it would take several months for the majority of Americans to be vaccinated.

The president’s new plan includes an ambitious goal of vaccinating 100 million Americans in the next 100 days. He has directed FEMA to set up federally-supported immunization centers around the country, plus expand vaccinations throughout pharmacies.

As part of the pandemic-related executive orders he signed on Thursday, one imposes new restrictions on both domestic and international travel. Inside the U.S., a mask order will apply to travel in airports and on planes, ships, intercity buses, trains and public transportation.

Travelers from abroad must furnish a negative COVID-19 test before departing for the U.S. and quarantine upon arrival. Biden has already mandated masks on federal property and has challenged Americans to “mask up” for 100 days to reduce virus spread.

Biden also addressed inequities in hard-hit minority communities as part of his executive actions Thursday.

A new order formalizes the establishment of a COVID-19 Health Equity Task Force to ensure that minority and underserved communities are not left out of the government's response. Blacks, Latinos and Native Americans have borne a heavy burden of death and disease from the virus. Surveys have shown vaccine hesitancy is high among African Americans, a problem the administration plans to address through an education campaign.

All of it is part of the Biden team’s new, 198-page national strategy released Thursday, along with a new COVID Response Team.

“I understand the despair and frustration of so many Americans and how they're feeling,” Biden said. “I understand why many governors, mayors, county officials, tribal leaders feel like they're left on their own without a clear national plan to get them through the crisis.”

Biden called on Americans to work together to follow new guidelines and tackle the worsening pandemic, a reiteration of his call for unity on Inauguration Day.

“We need to ask average Americans to do their part," said Jeff Zients, the White House official directing the national response. “Defeating the virus requires a coordinated nationwide effort."

But Biden officials say they're hampered by lack of cooperation from the Trump administration during the transition. They say they don’t have a complete understanding of their predecessors’ actions on vaccine distribution.

They're also depending on Congress to provide $1.9 trillion for economic relief and COVID-19 response. And they face a litany of complaints from states that say they are not getting enough vaccine even as they are being asked to vaccinate more categories of people.

Biden’s top medical adviser on COVID-19, Dr. Anthony Fauci, also announced renewed U.S. support for the World Health Organization after it faced blistering criticism from the Trump administration, laying out new commitments to tackle the coronavirus and other global health issues. Fauci said early Thursday that the U.S. will join the U.N. health agency’s efforts to bring vaccines, therapeutics and diagnostics to people in need, whether in rich or poor countries and will resume full funding and staffing support for WHO.

Although airlines, Amtrak and other transport providers now require masks, Biden's order makes it a federal mandate, leaving little wiggle room for passengers tempted to argue about their rights. It marks a sharp break with the culture of President Donald Trump's administration, under which masks were optional, and Trump made a point of going maskless and hosting big gatherings of like-minded supporters. Science has shown that masks, properly worn, cut down on coronavirus transmission.

Zients called Biden's goal of vaccinating 100 million people in his first three months “ambitious and achievable.”

The Democratic president has directed the Federal Emergency Management Agency to begin setting up vaccination centers, aiming to have 100 up and running in a month. He's ordering the Centers for Disease Control and Prevention to begin a program to make vaccines available through local pharmacies starting next month. And he's mobilizing the Public Health Service to deploy to assist localities in vaccinations.

Some independent experts say the administration should be setting a higher bar for itself than 100 million shots. During flu season, the U.S. is able to vaccinate about 3 million people a day, said Dr. Christopher Murray of the Institute for Health Metrics and Evaluation in Seattle. “Given the number of people dying from COVID, we could and should do more — like what we’re able to do on seasonal flu,” he said.

Zients said Biden will not follow through on a Trump administration plan to penalize states lagging in vaccination by shifting some of their allocation to more efficient states. “We are not looking to pit one state against another,” he said.

Biden has set a goal of having most K-8 schools reopen in his first 100 days, and he's ordering the departments of Education and Health and Human Services to provide clear guidance for reopening schools safely.

Getting schools and child care going will help to ease the drag on the U.S. economy, making it easier for parents to return to their jobs and restaurants to find lunch-time customers.

But administration officials stressed that reopening schools safely depends on increased testing.

To ramp up vaccination supplies, testing supplies and personal protective equipment, Biden is giving government agencies a green light to use a Cold War-era law called the Defense Production Act to direct manufacturing.

“We do not have nearly enough testing capacity in this country,” Zients said. “We need the money in order to really ramp up testing, which is so important to reopen schools and businesses.”

This means that any efforts to reopen the economy will hinge on how quickly lawmakers act on the $1.9 trillion package proposed by Biden, which includes separate planks such as $1,400 in direct payments to people, a $15 minimum wage and aid to state and local governments that some Republican lawmakers see as unnecessary for addressing the medical emergency.

The Biden plan estimates that a national vaccination strategy with expanded testing requires $160 billion, and he wants another $170 billion to aid the reopening of schools and universities.

There's also support for states in the package. Biden is ordering FEMA to reimburse states for the full cost of using their National Guards to set up vaccination centers. That includes the use of supplies and protective gear as well as personnel. States would also be able to tap FEMA's Disaster Relief Fund to help them get schools back open.

The Associated Press contributed to this report.