EXPLAINER - Why did the United States resettle only 12 Ukrainian refugees in March?

US President Joe Biden said last month that the United States would accept up to 100,000 Ukrainians fleeing Russia's invasion, but lawmakers and advocates have urged the Democratic president to speed up refugee and visa processing.

While several thousand Ukrainians have entered the United States via the border with Mexico and some on legal visas, only 12 Ukrainians came through the U.S. refugee program in March.

WHY HASN'T THE U.S. TAKEN IN MORE UKRAINIAN REFUGEES?

More than 4 million people have fled Ukraine to neighboring countries since Russia invaded the country on Feb. 24, according to United Nations data, touching off Europe's fastest-moving refugee crisis since the end of World War Two.

Top Biden officials said repeatedly last month that the vast majority of Ukrainian refugees would go to Europe during the conflict, which Russia calls a "special military operation."

But facing pressure from U.S. lawmakers and refugee advocates, the Biden administration said on March 24 that the United States would use "the full range of legal pathways" to accept up to 100,000 Ukrainians.

The pathways include the U.S. refugee resettlement program, which provides a road to citizenship, as well as existing visa avenues and a relief program known as "humanitarian parole," which allows people into the country on a temporary emergency basis.

The effort could stretch beyond the current fiscal year ending on Sept. 30, the official said, signaling that it may not move quickly. Refugee resettlement can take years and there is a long backlog for U.S. visa processing.

COULD THE U.S. ACCEPT MORE UKRAINIAN REFUGEES?

The United States admitted 514 Ukrainian refugees in January and February during Russia's build up to the war, according to State Department data, with only 12 resettled in March as the war intensified and the number of Ukrainians fleeing skyrocketed.

A State Department spokesperson said it had paused refugee operations in the Ukrainian capital of Kyiv but continued to process cases through an office in Chisinau, Moldova.

Many Ukrainian refugee applicants cleared for travel to the United States in March were set to depart from inside Ukraine, a person familiar with the matter told Reuters last month. Those cases were stalled by flight cancellations related to the conflict, leading to the near-shutdown of admissions, the person said.

Lawmakers and advocates have urged the Biden administration to accelerate the processing of Ukrainian applications saying too little has been done so far.

Biden set the overall refugee ceiling for this year at 125,000 after his predecessor Donald Trump, a Republican, slashed admissions to a record-low 15,000, which gutted the program and led to processing delays already worsened by the COVID-19 pandemic.

WHAT HAPPENS TO UKRAINIANS WHO TRY TO ENTER THE UNITED STATES FROM MEXICO?

Thousands of Ukrainians and Russians have been traveling to the U.S.-Mexico border to seek asylum, a trend that could accelerate as the humanitarian crisis worsens.

Last week, about 3,000 Ukrainians deemed by U.S. authorities to be particularly vulnerable were allowed to cross the border into the United States, according to the U.S. Department of Homeland Security (DHS).

The circuitous route may be the most accessible pathway into the United States for Ukrainians at the moment, even as it requires them to enter Mexico on tourist visas and approach the border without assurances they will be allowed to enter.

As of Thursday, about 2,400 Ukrainians were in Tijuana, Mexico, waiting to cross into the United States, according to Enrique Lucero, the city's migration affairs director.

HOW ELSE ARE UKRAINIANS ENTERING THE UNITED STATES?

The U.S. State Department declined to provide statistics on visas issued to Ukrainians in March and DHS did not say how many Ukrainians entered the United States during that period.

About 200 Ukrainians were issued immigrant visas in February while nearly 1,500 were issued temporary non-immigrant visas, according State Department data, though most of those visas were likely approved before Russia invaded Ukraine on late February.

The State Department said that visa applicants in general may face longer wait times at some U.S. embassies and consulates due to the COVID-19 pandemic.

Ukrainians, just like other applicants, can request faster processing if circumstances warrant it, the department said, stressing that refugees should not attempt to enter the United States on tourist visas or other temporary visas.

More than 350 Ukrainians have sought humanitarian parole to enter the United States from abroad since the start of the conflict, according to a person familiar with the matter. Separately, 28 applications were approved for entries related to medical care for children, the person said.

IF THE U.S. ISN'T ACCEPTING MANY UKRAINIAN REFUGEES, WHAT IS IT DOING?

The U.S. government is devoting significant economic aid to assist the European countries receiving refugees.

Biden pledged $1 billion in new humanitarian aid for those affected by the war during his visit to Europe in late March.

Earlier that month, Biden signed into law a spending bill that provides $13.6 billion to help Ukraine and European allies, including about $4 billion to aid people fleeing.

The U.S. government also announced in March that it will grant Temporary Protected Status (TPS) to an estimated 75,000 Ukrainians already in the United States but it would not apply to people who arrived after March 1.

In a bipartisan letter this week, 65 lawmakers in the U.S. House of Representatives called on Biden to make a technical change to the TPS designation that would include more recently arrived Ukrainians.

READ MORE: Latest development on Ukraine-Russia crisis