WASHINGTON (REUTERS, AFP) - President Donald Trump lifted a US travel ban on citizens from Chad on Tuesday (April 10) after a six-month US government review found improvements in the African country's security standards, the White House said.

The Trump administration added Chad to a revamped travel ban list in September after it said the Chadian government had failed to send proof it had taken adequate security measures to prevent terrorists from travelling to the United States.

"The President announced today that Chad has raised its security standards to meet important baseline US national security requirements," the Department of Homeland Security announced.

"Therefore, its nationals will again be able to receive visas for travel to the United States."

The travel restrictions will be officially terminated on April 13.

The central African country's government, which the US calls a "critical" partner in fighting terrorism, had expressed astonishment in September last year when the US unexpectedly added it to five other mainly-Muslim countries that the Trump administration place under a travel ban.

The DHS has always maintained that the ban focused on getting countries to improve information on their citizens and cooperation on travel databases, to meet US security standards.

US officials said Chad has addressed the deficiencies in vetting outward bound travellers and cooperating with US security bodies.

With Chad taken off the list, seven countries - Iran, Libya, Syria, Yemen, Somalia, North Korea and Venezuela - are still subject to the travel restrictions.

Mr Trump's critics have said his travel ban unfairly singled out Muslims, and violated US law and the Constitution.

Courts struck down the first two versions of Mr Trump's travel ban, and the current one is narrower in scope than its predecessors.

The US Supreme Court will consider its legality this spring, and a decision is expected in June.