U.S. Secretary of State John Kerry travels on Tuesday to the Philippines, where Washington is negotiating a deal to expand its military presence.
The trip follows a stop in Vietnam, where Kerry pledged over $32 million to help Southeast Asian countries protect their territorial waters amid tensions with China.
Kerry denied the new assistance is in response to aggressive Chinese maritime behavior, adding that the U.S. supports diplomacy, not unilateral actions, in resolving the disputes.
"Peace and stability in the South China Sea is a top priority for us and for countries in the region. We are very concerned by and strongly opposed to coercive and aggressive tactics to advance territorial claims," said Kerry.
Under the deal, the U.S. will provide Vietnam $18 million, including five fast patrol boats for its Coast Guard. Others in the Association of Southeast Asian Nations will receive $14.5 million.
In Manila, Kerry hopes to use his meetings on Tuesday with Philippine leaders to make progress on a deal allowing more U.S. troops, aircraft and ships to pass through the country.
On Wednesday, Kerry will tour areas hit last month by Typhoon Haiyan, which killed thousands of people and prompted a massive, military-led humanitarian response by the United States.
The U.S. spent millions of dollars and sent an aircraft carrier group and a thousand Marines to help its former colony recover from the typhoon, an effort many analysts said could help lead to closer defense ties.
Manila is involved in a bitter dispute with China over territory in the South China Sea. Following a weeks-long standoff last year, the Philippines lost control of an uninhabited, but strategic, reef in the area.
China also has disputes with other nations in the region, including Vietnam, in the South China Sea, which contains rich fishing grounds, vital shipping lanes and vast untapped energy deposits.
During his trip, Kerry has continued to insist that the U.S. does not take sides in the disputes, even while he has expanded military cooperation with China's neighbors and warned against Chinese aggressiveness.
On Monday, Kerry again said China should not implement its new Air Defense Identification Zone, which includes disputed areas claimed by Japan and South Korea, in the East China Sea. He also said Beijing "should refrain from taking similar unilateral actions elsewhere, particularly in the South China Sea."
The U.S. has refused to recognize the Chinese zone. It has run B-52 bombers on what were described as routine training missions that deliberately ignored Chinese demands to submit flight plans and identify themselves.
The incidents have raised fears of a military clash. Those fears were heightened earlier this month when U.S. officials said one of its ships, the USS Cowpens, nearly collided with a Chinese vessel in the South China Sea.
The U.S. military says its ship, operating in international waters, was forced to take evasive action to avoid hitting the Chinese vessel, which was traveling with China's new aircraft carrier, the Liaoning. There has been no official comment from China on the incident.
China has steadily increased its military spending and naval activity in recent years, but says its efforts are aimed only at peace and protecting its territory. It views the renewed U.S. military presence in Asia as an effort to contain it, an accusation Washington denies.