File Photo: A member of the Al Murisi family, Yemeni nationals who were denied entry into the U.S. because of the travel ban, shows the cancelled visa in their passport from their failed entry to reporters as they successfully arrive to be reunited with their family at Washington Dulles International Airport in Chantilly, Virginia, U.S., February 6, 2017. (Xinhua/REUTERS)

WASHINGTON, Sept. 13 (Xinhua) -- The United States has issued visa restrictions on Cambodia, Eritrea, Guinea and Sierra Leone that have refused to take back deported citizens.

The visa restrictions, effective on Wednesday, affected "certain categories of visa applicants, determined on a country-by-country basis," the Department of Homeland Security said in a statement Wednesday.

"Without an appropriate response from the impacted countries, the scope of these sanctions may be expanded to a wider population," it warned.

As stipulated by the visa restrictions, the U.S. Embassy in Eritrea has stopped issuing B visas for all visitors for business or pleasure, and officials of the other three countries were targeted by the visa sanctions.

"These four countries have not established reliable processes for issuing travel documents to their nationals ordered removed from the United States," said the statement.

About 2,137 Guinean and 831 Sierra Leone nationals, many with serious criminal convictions, have been released into the United States, it added.

Another 700 Eritrean nationals and more than 1,900 Cambodian nationals are currently subject to a final order of removal.