"And numerous leaders who do not attend do so because they have internal issues, which prevents them from coming", Mr. Paynor also said.
Paynor said that while security measures have been in place, officials in charge for Asean summit are also considering Duterte's instruction to maintain "normal flow of daily activities" in Manila during the four-day long Asean meetings.
In a phone call in December previous year, President Duterte invited then President-elect Trump to the ASEAN Summit.
Ambassador Marciano Paynor Jr., director-general for operations of the ASEAN 2017 National Organizing Council, said Trump confirmed his attendance verbally during a phone conversation with President Duterte last November.
"I do not know but he seems to be very busy".
The series of activities for the ASEAN Summit involve a total of 137 meetings, two summits, 17 ministerial meetings, 42 senior officials' meetings and 76 meetings of technical working groups.
This vote of confidence was indeed warmly welcomed by ASEAN officials, as the White House had finally given "very positive indications" about U.S. interests in the region, outgoing Indonesian permanent representative to ASEAN Rahmat Pramono said.More news: Secret Service limits sidewalk access south of White House
"Multilateral meetings of this sort, we usually expect 100 percent attendance", Paynor added. "Numerous leaders who do not attend do so because of internal issues", although "one or two" leaders may not be able to attend.
On April 26-29, leaders of ASEAN member countries are set to attend the 30th ASEAN Summit and Related Meetings in Manila.
Leaders from New Zealand, South Korea, the US, Japan, Australia, China are expected at the meeting, along with representatives from ASEAN's 9 other member states.
He said other Asean leaders may have a "pull-aside" with the President, if their request for a bilateral meeting would not push through.
President Rodrigo Duterte will welcome next week Sultan Hassanal Bolkiah of Brunei and President Joko Widodo of Indonesia for a formal bilateral meeting.
The Indonesian president is expected to attend the launch of the Davao-General Santos-Bitung roll-on, roll-off route in Davao City on April 30.