WASHINGTON—The Trump administration plans to add seven countries to a group of nations subject to travel restrictions, including Nigeria, Africa’s most populous country, along with others in Africa and Asia, according to administration officials who have seen the list.

The new restrictions would apply to travelers and immigrants from Belarus, Eritrea, Kyrgyzstan, Myanmar, Nigeria, Sudan and Tanzania. The countries wouldn’t necessarily face blanket bans on travel to the U.S., but could have restrictions placed on specific types...