U.S. Secretary of State John Kerry directly called on China Thursday to stop building artificial islands in the South China Sea and halt construction efforts on the disputed lands.
During a regional forum of the Association of Southeast Asian Nations (ASEAN) in Malaysia this week, diplomats again struggled to agree on a joint statement on the territorial dispute.
Kerry called it “essential” to maintain freedom of navigation and overflight in the region.
"Despite assurances that these freedoms will be respected, we have seen warnings issued and restrictions attempted in recent months. Let me be clear: The United States will not accept restrictions on freedom of navigation and overflight, or other lawful uses of the sea,” he said.
Kerry urged the countries to commit to stop the construction and militarization of features in the region to lower tensions.
Growing regional tensions
China, Vietnam, Malaysia, Taiwan and the Philippines have overlapping claims in the remote seas that are vital shipping lanes and fishing grounds. But this year Beijing rapidly ramped-up land reclamation efforts and built an airstrip to shore-up its claim.
On Wednesday, China Foreign Minister Wang Yi said his country had stopped its land reclamation projects on the waterway. Kerry said he hopes that is true, but has not confirmed it.
"What's really needed though is an agreement to stop not just the reclamation but the large-scale construction and militarization."
ASEAN foreign ministers Thursday agreed to back the Iran nuclear deal, known as the Joint Comprehensive Plan of Action (JCPOA).
In a Thursday statement, ministers said if the deal is fully implemented, it will “contribute to building confidence in the exclusively peaceful nature of Iran’s nuclear program."
Kerry marked the 70th anniversary of the U.S. nuclear bombing of Hiroshima, on Thursday, likening the impact of the event to the significance of the Iran nuclear deal.
"It is impossible not to have thoughts about it," said Kerry, as he sat down for talks with Japanese Foreign Minister Fumio Kishida on the sidelines of the ASEAN forum.
"Needless to say, it is a very, very powerful reminder of not just the impact of war lasting today on people and countries, but it also underscores the importance of the agreement we have reached with Iran to reduce the possibility of more nuclear weapons," he added.
An estimated 140,000 people were killed as a result of the August 6, 1945, bombing of the Japanese city of Hiroshima. An additional 70,000 were killed when U.S. planes dropped an atomic bomb on the city of Nagaski three days later.
The U.S. and its allies said the bombings helped bring an end to World War Two.
US, Russia meeting
Kerry also said that he and Russian Foreign Minister Sergei Lavrov spoke about an agreement to investigate chemical weapons attacks in Syria.
Kerry said that they agreed on the language of a new U.N. Security Council resolution that would lead to investigations into who is responsible for the attacks, and he believes the process will allow investigators to hold perpetrators accountable.
Foreign ministers and senior officials from 26 countries attending the ASEAN forum also addressed a range of other issues, including cybersecurity, disaster relief and environmental protection.
The State Department said Kerry also announced a USAID oceans and fisheries partnership, with an initial commitment of over $4 million to help address the threat of illegal and unregulated fishing in Southeast Asia.
Kerry also announced that the United States will provide $600,000 in disaster assistance to Myanmar, where the Red Cross estimates that floods and landslides have now affected nearly 180,000 people.
Kerry is nearing the end of a five-nation tour that has also included stops in Egypt, Qatar and Singapore.
Kerry in Vietnam
Later Thursday, he travels to Vietnam, where he will mark the 20th anniversary of renewed bilateral ties that were severed four decades ago as the protracted Vietnam War came to an end.
Over the years, the United States and Vietnam have forged strong economic ties, with two-way trade topping $36 billion last year.
Both countries are part of negotiations for the Trans-Pacific Partnership, a massive 12-nation trade deal.
However, the United States has continued to raise concerns about Vietnam's human rights record, including its detention of dissidents.
In July, U.S. President Barack Obama hosted Vietnamese Communist party General Secretary Nguyen Phu Trong at the White House.
WATCH: VOA's Pam Dockins in Kuala Lumpur