MANILA, March 22 (Reuters) - Philippine President Ferdinand Marcos Jr said on Wednesday he will make a formal announcement soon on the locations of four additional military bases under the Enchanced Defense Cooperation Agreement (EDCA) with the United States.

Marcos last month granted the United States access to four sites, on top of five existing locations under the 2014 EDCA, which comes amid China's increasing assertiveness towards the South China Sea and self-ruled Taiwan.

"There are four extra sites scattered around the Philippines. There are some in the north there are some around Palawan there are some further south," Marcos told reporters at the sidelines of the Philippine army's founding anniversary.

EDCA allows U.S. access to Philippine bases for joint training, pre-positioning of equipment and building of facilities such as runways, fuel storage and military housing, but it is not a permanent presence.

Speaking before Philippine troops, Marcos told them to be vigilant as he said that the external threat to his country's security was becoming more "complex" and "unpredictable."

"Be vigilant against elements that will undermine our hard earned peace, our hard earned stability, continue to improve relations with your counterparts overseas," Marcos said.

Marcos said he was aware of an "emerging threat" to his country's territory, which he said would require "adjustments in our strategy."

The Philippine leader did not give specifics, but he has previously cited the need to look beyond internal threats to security.

"The external security environment is becoming more complex. It is becoming more unpredictable," Marcos said.