The Republic of Palau has asked the Pentagon to build ports, bases and airfields on the island nation, officials said, offering a boost to U.S. military expansion plans in Asia, as Washington aims to counter China.

The request came during a visit here last week by Defense Secretary Mark Esper, the first-ever trip by a U.S. Pentagon chief to the tiny republic, which is made up of hundreds of islands in the Philippine Sea and is closely aligned diplomatically with Taiwan…

Palauan President Tommy Remengesau Jr. visited the White House last year with counterparts from Micronesia and the Marshall Islands, adopting a joint statement on security in a show of unity.

Last week, Mr. Remengesau handed Mr. Esper a letter requesting that the U.S. enter into a broader, longer-term relationship with the island nation, where the U.S. has had a small but permanent presence for decades. The Palauans said they think the republic has been underused by the U.S. military for years.