The United States will upgrade and build facilities on Philippine military bases this year, Manila's defense minister said on Thursday, bolstering an alliance strained by President Rodrigo Duterte's opposition to a U.S. troop presence.

The Pentagon gave the green light to start the work as part of an Enhanced Defense Cooperation Agreement (EDCA), a 2014 pact that Duterte has threatened to scrap during barrages of hostility towards the former colonial power.

"EDCA is still on," Defense Secretary Delfin Lorenzana told a news conference.