"As part of our commitment to advancing regional security in the Indo-Pacific, the United States is excited to announce almost US$300 million dollars of new funding to reinforce security cooperation throughout the entire region", he said.
Trump, who has accused China and others of exploiting the United States in global trade, has demanded that Beijing make a host of concessions to avoid the new duties, which could be imposed in the weeks after a comment period closes on September 5.
China, however, shows no sign of bending to Washington's pressure.
The US Secretary of State Mike Pompeo is due in Singapore on Friday fresh from unveiling an investment pitch for the region, although many ASEAN members could be more concerned with a US-China trade that threatens to jolt their economies.
"The code of conduct is meant to... ensure that peace, stability, confidence is built up so that we can continue to make collective progress between Asean and China while we take time to resolve the territorial disputes", he said on Thursday.
Singapore is now country coordinator for Asean-China relations, but is set to hand over its role to the Philippines. "That says a lot for governance and democracy", the senior State Department official added.
Malaysia, Brunei, Vietnam and the Philippines all claim some or all of the South China Sea and its myriad shoals, reefs and islands.
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In the draft text, Beijing suggests that China and the 10 Asean states should carry out joint military exercises regularly.
Earlier, China has proposed to conduct military exercises and energy exploration with ASEAN countries in the South China Sea, planning to exclude the United States.
The suggestion to exclude outside countries "is obviously targeted at the United States, which has been dominating the waters of the Western Pacific and the South China Sea in particular", said Hoang Thi Ha of the ISEAS-Yusof Ishak Institute's ASEAN Studies Centre in Singapore.
China and ASEAN have held talks for years to try to ease tensions and prevent the disputes from degenerating into open conflicts.
However, opposition has weakened in other parts of Southeast Asia, with analysts saying that countries are keen to attract Chinese investment and are anxious about United States commitment to the region under President Donald Trump.