US Secretary of State John Kerry flew on Monday into a row with the European Union over allegations that Washington spied on its allies, as he took part in a forum aimed at building security in the Asia-Pacific.
Kerry went straight from four days of intensive diplomacy in the Middle East to a meeting hosted by Southeast Asian nations in the gas-rich sultanate of Brunei, where South China Sea disputes and North Korea were also set to dominate talks.
Kerry was due to hold a series of direct meetings with counterparts from world powers on the sidelines of the forum, which ends on Tuesday with a gathering of 26 Asia-Pacific countries and the European Union.
One of the first was with European Union foreign policy chief Catherine Ashton, which was expected to be dominated by explosive allegations from fugitive leaker Edward Snowden that Washington bugged EU offices.
European allies have demanded answers from the United States on the claims, reported by German weekly Der Spiegel, and warned relations would be damaged if the allegations proved to be true.
"We can't negotiate a large transatlantic market if there is any doubt that our partners are bugging the offices of European negotiators," EU Justice Commissioner Viviane Reding said.
One document, dated September 2010 and classed as "strictly confidential", describes how the National Security Agency kept tabs on the EU's mission in Washington, Der Spiegel said.
Microphones were installed in the building and the computer network was infiltrated, giving the agency access to emails and internal documents.
The United States said Sunday it would respond to the EU via diplomatic channels over the bugging allegations.
The Snowden affair is also likely to come up when Kerry holds talks with Russian Foreign Minister Sergei Lavrov in Brunei on Tuesday.
Washington is angry that Snowden, a former government contractor wanted by the United States after divulging details of the widespread surveillance on communications, flew to Moscow from Hong Kong as he sought asylum, possibly in Ecuador.
Russia has refused to hand Snowden over.
However Kerry said the main focus for the Lavrov talks would be the Syrian war.
"I'm actually anxious to get there (Brunei) and to engage with him because the situation in Syria is grave," Kerry told reporters in Tel Aviv before flying to Asia.
"Part of my conversation with Foreign Minister Lavrov and with the Russians will be how we can maximise our efforts together to have an impact on this."
Moscow is a key supporter of embattled Syrian President Bashar al-Assad, while Kerry has been working with Gulf Arab states to step up assistance to the opposition.
Away from Kerry's sideline encounters, the official meetings in Brunei are likely to revolve in large part around regional concerns over China's rise.
During initial talks on Sunday among the 10-member Association of Southeast Asian Nations (ASEAN), the Philippines accused China of a "massive" military buildup in the disputed South China Sea, which it said threatened peace.
China, which claims virtually all of the strategic waterway, has been at odds with rival claimants, particularly the Philippines and Vietnam. This has led to tense confrontations at sea and allegations of Chinese bullying.
In opening comments at a meeting with his ASEAN counterparts on Monday, Kerry called for quick progress on a long-delayed code of conduct between China and Southeast Asian Nations for the disputed waterway.
"We very much hope to see progress on a substantive code of conduct to help ensure stability in this vital region," Kerry said.
Temperatures have also risen in the East China Sea amid rival claims by Beijing and Tokyo to remote uninhabited islands.
Kerry was scheduled on Monday to meet his Japanese and South Korean counterparts, as well as Chinese Foreign Minister Wang Yi.
North Korea's nuclear programme was expected to be a top focus at those meetings, after the isolated country carried out its third underground atomic test in February and made a series of dire warnings of war.
All foreign ministers from the long-running but currently stalled six-nation talks aimed at persuading North Korea to give up its nuclear weapons are in Brunei.
But the United States has ruled out a direct meeting between Kerry and North Korean Foreign Minister Pak Ui-Chun.