U.S. President Donald Trump issued an expanded version of his travel ban on Friday that targets prospective immigrants from Nigeria and five other countries, a move that could affect thousands of people and reignite debate on whether the policy is discriminatory.

Of the six countries added to the ban, four are African nations and three have Muslim-majority populations. Democrats and immigration advocates accuse the Trump administration of seeking to expand its original 2017 ban that targeted Muslim-majority countries and of disproportionately focusing on African countries.

Read more:

How Trump's 2017 travel ban dashes one Iranian's dreams

Acting Homeland Security Secretary Chad Wolf said during a call with reporters that the six countries failed to meet U.S. security and information-sharing standards, which necessitated the new restrictions. The problems Wolf cited ranged from sub-par passport technology to a failure to sufficiently exchange information on terrorism suspects and criminals.

Belarus, which had been under consideration for inclusion, took steps to remedy deficiencies in recent months and will not face visa restrictions, Wolf said.

The United States will suspend the issuance of visas that can lead to permanent residency for nationals of Eritrea, Kyrgyzstan, Myanmar and Nigeria, a presidential proclamation said. Temporary visas for tourists, businesspeople, students and workers from those nations will not be affected, it said.

The U.S. government also will stop issuing“diversity visas” to nationals of Sudan and Tanzania, the proclamation said. The visas, which Trump has criticized, are available by lottery for applicants from countries with low rates of immigration.

“These countries, for the most part, want to be helpful,” Wolf said, “but for a variety of different reasons simply failed to meet those minimum requirements that we laid out.”

The original travel ban barred nearly all immigrants and travelers from seven countries with majority Muslim populations. The policy was revised amid court challenges, but the U.S. Supreme Court ultimately upheld it in June 2018.

Trump has made cracking down on immigration a focus of his 2020 re-election campaign. His travel ban policy is popular with Republican supporters.

The existing version of the ban includes Iran, Libya, Somalia, Syria and Yemen. The Democratic People's Republic of Korea (DPRK) and Venezuela also face visa bars, but those measures affect relatively few travelers. Those restrictions will remain in place.

The new travel ban will take effect on February 21, according to the proclamation.