The Biden administration is expected soon to announce new details on how Ukrainian refugees would be able to seek entry into the United States on humanitarian grounds, a source familiar with the planning says.

The move comes nearly one month after US President Joe Biden pledged to admit up to 100,000 Ukrainians fleeing the invasion.

Over 5,000 Ukrainians attempted to gain entry into the US in March, including 3,274 at the southern border with Mexico, according to US Customs and Border Protection data.

The humanitarian parole program, which would fall under the umbrella of the Department of Homeland Security and could be announced as soon as Thursday, would require Ukrainians seeking entry to the US to be sponsored by a US citizen or individual, which would include resettlement organizations and non-profits, the source said.

The individuals would need to undergo rigorous security vetting and checks — including biographic and biometric screening and complete vaccinations and other public health requirements, such as receiving the Covid-19 vaccine — in order to be eligible, the source said.

Sponsors would need to pass security background checks of their own as well as declare financial support.

Through this process, Ukrainian applicants would be allowed to travel to the US and be considered for humanitarian parole on a case-by-case basis for up to two years, the source said. If accepted, the individuals would be eligible for work authorization.

The Biden administration could begin taking applications for the program as soon as before the end of April, according to the source.

In addition to the humanitarian parole program, the State Department is working to expand its Refugee Admissions Program operations in Europe, the source added, with the goal of providing eligible individuals with better access to the Lautenberg program — an 1989 initiative aimed at helping those fleeing religious persecution from the Soviet Union — as well as stepping up referral mechanisms for Ukrainians seeking permanent resettlement.

White House Press Secretary Jen Psaki told reporters Wednesday that the administration was working to finalize the details of how it would welcome up to 100,000 Ukrainian refugees to the US.

A White House spokesperson declined to comment on the new details but said additional details about the administration’s efforts would be announced “soon.” The Department of Homeland Security did not immediately reply to a request for comment.

More than five million people have fled Ukraine since Russia’s invasion began in late February, the United Nations High Commissioner for Refugees said Wednesday.

The Prime Ministers of Spain and Denmark arrived in Kyiv on Thursday to meet with Ukrainian President Volodymyr Zelensky, their respective offices said.

After arriving in the Ukrainian capital, Spanish Prime Minister Pedro Sanchez and Danish Prime Minister Mette Frederiksen appeared together in a short video tweeted by Sanchez’s official account.

“Ukraine has the support, solidarity and commitment of Spain,” the post said.

Frederiksen’s office tweeted that she and Sanchez would “meet with President Zelensky to deliver concrete support to Ukraine.”

“Tthey will meet to discuss the current situation in Ukraine, further support for the Ukrainians and the prosecution of war crimes and human rights violations in connection with the Russian invasion,” Frederiksen’s office said in a statement.

Russia has denied allegations of war crimes and claims its forces do not target civilians, but CNN journalists on the ground in Ukraine have seen firsthand evidence of atrocities at multiple locations across the country.

Sanchez announced earlier this week that Spain would reopen its embassy in Kyiv in the coming days, which it had closed shortly after Russia’s invasion of Ukraine in late February.