SINGAPORE, May 21 (Reuters) - The United States is expected to reach a deal on the long-term framework for an economic security zone with the Philippines "sooner rather than later", a senior U.S. official said on Thursday.

As Washington aggressively expands its technology supply chain alliance known as "Pax Silica", the official, Jacob Helberg, said both countries have a two-year window to work out the arrangements under a pact they signed last month.

Both parties will also set sectoral industrial priorities for the kinds of economic activities in the zone, Helberg, the U.S. undersecretary of state for economic affairs, told Reuters in an interview. 

"I expect the United States and the Philippines to reach a deal sooner rather than later," he said, adding, "There's an enormous amount of momentum behind this."

Last month's agreement makes the Philippines the 13th country to join Pax Silica, a programme seeking to safeguard the full technology supply chain, from critical minerals and advanced manufacturing to computing and data infrastructure.

Helberg said the alliance has since grown rapidly to 15 members from seven founding members last September. 

"We will most likely be at 16 by the end of next month, because we're probably going to add one or two members over the next four weeks," he added.

While Washington is pushing ahead with the framework, the Philippines has not agreed to its request seeking diplomatic immunity for the zone, the Philippines' development authority chief told Bloomberg on Monday.

Helberg visited a proposed 4,000-acre (1,620-hectare) site in New Clark City north of the capital Manila on Monday, joined by representatives of more than a dozen U.S. companies, such as 8VC, Agility Robotics, Joby Aviation and Valar Atomics.

Young Liu, chairman of the world's largest contract electronics maker Foxconn, was also among the delegation, a photograph posted on X showed. 

Helberg told Reuters that while it was early, there was a high level of interest, both from the companies which attended and other U.S. firms.

He was speaking at the ATX summit in Singapore, where he met digital ministers for the 11-member regional grouping, the Association of Southeast Asian Nations.  

Helberg said he talked to the Singaporeans and "a number of others" on opportunities in minerals and logistics.