President Donald Trump has issued a new travel ban that saw North Korea, Venezuela and Chad among a list of eight countries cited for poor security and lack of cooperation with US authorities.

"Making America Safe is my number one priority. We will not admit those into our country we cannot safely vet," Trump said in a tweet.

Full travel bans were placed on nationals from North Korea and Chad, while the restrictions for Venezuela were limited to officials from a long list of government agencies and their families.

Chad was added to the list even though Trump's order called it "an important and valuable counterterrorism partner."

Venezuela, in a political and economic crisis due to its embattled, increasingly oppressive regime, was listed for a limited ban.

Other countries included in the ban were Iran, Libya, Somalia, Syria and Yemen.

Speaking on background, government officials said the addition of North Korea and Venezuela demonstrated that the measure was set on the basis of security and was not a "Muslim ban," as detractors have argued.

The bans for the five countries from the previous 90-day order, which expired Sunday, would immediately continue under the new order. For North Korea, Chad, and Venezuela, the restrictions will be implemented starting October 18.