President Rodrigo Duterte has returned to Manila following his "fruitful" participation in the 35th ASEAN Summit and Related Summits in Thailand.

Duterte arrived at the Villamor Air Base in Pasay City on Monday night after taking part in a series of interactive discussions with his counterparts in the ASEAN and Dialogue Partners.

In a statement on Tuesday, Malacanang said Duterte, during the summits, stressed that the Philippines, as Country Coordinator of the ASEAN-China Dialogue, would do its "utmost to conclude negotiations on a Code of Conduct (COC) (in South China Sea) as soon as possible.

"An effective and substantive COC is essential to maintaining peace and stability in the region," Palace said.

It said that Duterte also raised his concern over the ongoing trade tension between key partners that could slow down growth, thus, undermining food security and poverty alleviation efforts.

"He (Duterte) called for an open, fair and rules-based international trading system," Malacanang said.

Duterte also underscored the need for the early conclusion of the negotiations on the Regional Comprehensive Economic Partnership.

In a text message, Trade Secretary Ramon Lopez, who represented Duterte in RCEP summit on Monday in Thailand, said that 15 out of 16 countries have concluded the RCEP after threshing out all the issues.

"India now open to be identified as the one RCEP country that has pending issues on rules and market access, it is now clear only the 15 countries concluded for now since India has until next year to settle (its) remaining issues, and decide if (it) can still sign with the 15 countries next year," he said.

"So the assumption now is that they are in, but must settle outstanding issues, and that we all want the 16 to sign next year," Lopez added.

India has refused to agree on RCEP as this would place Indian businesses and agriculture on unequal competition with other countries.

The 16 countries negotiating for the RCEP include the 10 ASEAN members, namely Brunei Darussalam, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Thailand, and Vietnam, plus Australia, China, India, Japan, New Zealand and South Korea. Celerina Monte/DMS