By Adam Entous
SINGAPORE (Reuters) - The United States said on Saturday it was weighing new options beyond the United Nations to punish North Korea, which South Korea blames for the sinking of a warship that has escalated tensions on the peninsula.
Seoul has complained to the U.N. Security Council over the sinking of the corvette Cheonan in March, which killed 46 sailors. South Korea and its main ally, the United States, accuse the reclusive North of torpedoing the ship, although it is unclear what concrete action, if any, the U.N. will take.
U.S. Defense Secretary Robert Gates told a security conference in Singapore it was the "collective responsibility" of Asian states to address North Korean "provocations," increasing pressure on a reluctant China to rebuke its ally.
"To do nothing would set the wrong precedent," Gates said at a meeting with his South Korean and Japanese counterparts.
"One has to wonder what they (the North Koreans) were thinking," he told the BBC in an interview, "and whether there are other provocations to come."
Gates said Washington would conduct more joint exercises with South Korea and support "action" by the Security Council.
"At the same time, we are assessing additional options to hold North Korea accountable," he said, suggesting the United States and its allies could act unilaterally or in concert.
Officials said Washington was looking at options including tightening economic sanctions, expanding searches of North Korean vessels and holding more large-scale shows of military force to try to deter future attacks.
North Korea denies responsibility for sinking the Cheonan and accuses South Korean President Lee Myung-bak of staging the incident to help his chances in local elections this week.
In increasingly shrill rhetoric, the North has warned several times that "war could break out at any moment."
Lee pledged to clamp down on any action deemed threatening but dismissed the likelihood of open conflict.
"There is no possibility of a war. There has been occasionally and locally peace-threatening behavior but we will strongly suppress it," Lee's spokesman, contacted by telephone, quoted him as telling businessmen at the Singapore summit.
U.S. military officials, including Admiral Robert Willard, head of the U.S. Pacific Command, have also played down the risk of a major conflict, saying there were no signs North Korea was preparing a nuclear test or moving troops toward the South.
But officials said another attack could not be ruled out. "When you're dealing with a regime as unpredictable as (North Korea), that is always a concern," Morrell said.
Diplomats said that in talks with Asian leaders, Gates and other officials had made it very clear their goal is to avoid an escalation.
The United States and South Korea face a difficult balancing act -- finding a way to punish the North without provoking another attack. Gates raised the possibility that Seoul would stop short of seeking a full-blown Security Council resolution.
Planned U.S.-South Korea military drills might also be put off, at least until it becomes clear what action the United Nations is prepared to take, officials said.
The big question facing the United States, South Korea and Japan is how to gain leverage over a regime that appears to be indifferent to international pressure and responds in such seemingly erratic ways.
China, North Korea's only major ally and benefactor, may be the central player, although some U.S. intelligence officials have questioned how much sway it really has.
As a permanent member of the Security Council, China can veto any U.N. resolution or statement chastising the North.
Without referring to China by name, Gates pointedly told Asian leaders in Singapore that all the nations in the region "share the task of addressing these dangerous provocations."
"Inaction would amount to an abdication of our collective responsibility to protect the peace and reinforce stability in Asia," he said.
Beijing has so far declined publicly to join international condemnation of Pyongyang, saying it is assessing the evidence.
U.S. officials acknowledge that China appears reluctant to embrace tough measures at the United Nations.
Likewise, Russia has yet to fully sign on to South Korea's version of events about the sinking, they cautioned.
Beijing broke off military ties with Washington after it told Congress in January of a plan to sell up to $6.4 billion of arms to Taiwan, which Beijing regards as a renegade state.
At the annual conference, known as the Shangri-La Dialogue, Gates urged Beijing to accept the "reality" that Washington is committed to arming Taiwan, like it or not.
That drew a sharp challenge from Major General Zhu Chenghu of China's National Defense University. He said continued arms sales to Taiwan sent the message that America saw the Chinese as "enemies." Gates rejected that characterization, saying China and the United States were partners in many areas.
(Additional reporting by Harry Suhartono and Nopporn Wong-Anan in SINGAPORE, and Kim Yeon-hee in SEOUL; Editing by Kevin Liffey)