US President Barack Obama asked Congress to ratify contentious UN maritime rules Thursday, hoping to strengthen his hand in a dangerous stand-off with Beijing over the disputed South China Sea.

Addressing the US Air Force Academy in Colorado, Obama said that Congress should approve UN rules designed to peacefully resolve maritime disputes.

Obama's presidency has seen escalating diplomatic and military tensions over Beijing's claim to territory throughout the South China Sea.

The area is a vital shipping channel that is also believed to have significant energy and mineral deposits.

It is also pivotal to China's effort to transform the focus of its navy from coastal defense to a "blue water navy" capable of projecting power across the region.

Chinese military deployments in the South China Sea have spooked neighbors who also claim islands and atolls, and set off a chain of tit-for-tat countermeasures by Washington.

Obama has ordered US navy vessels to sail across the region to affirm freedom of navigation.

The White House believes that Congress's failure to ratify the UN agreement has undercut the US case that disputes must be solved peacefully.

"If we are truly concerned about China's actions in the South China Sea for example, the Senate should help strengthen our case by approving the law of the sea convention," Obama said.

Obama's call comes at a particularly sensitive time, ahead of a landmark international panel ruling on a dispute between the Philippines and China over the Spratly Islands.

Beijing has angrily rejected the panel's jurisdiction and vowed to ignore its ruling.

Four topics to dominate Singapore security forum
Singapore (AFP) June 2, 2016 - Defence ministers and military chiefs from around the world are attending Asia's largest annual security forum starting Friday in Singapore.

Known as the Shangri-La Dialogue, it will start with a keynote address by Thailand's Prime Minister Prayut Chan-O-Cha and will end on Sunday after a series of open and closed-door talks.

The forum is organised by the London-based International Institute for Strategic Studies.

Here are four key topics likely to dominate discussions:

- South China Sea -

Regional neighbours and other powers are fretting over what they see as China's expansionism as it rushes to exert sovereignty over the vast waters, a major global shipping route believed to be home to large oil and gas reserves.

Four Southeast Asian states -- the Philippines, Vietnam, Malaysia and Brunei -- have rival claims with China, which claims nearly all of the sea based on controversial historical maps.

The Philippines has filed a case against China before the Permanent Court of Arbitration in The Hague and a decision is expected in the coming weeks but China has said it will not recognise any ruling.

- North Korea -

The UN Security Council has strongly condemned North Korea's attempted missile launches this week and in April, urging governments to ramp up efforts to impose sanctions on Pyongyang.

UN resolutions ban North Korea from any use of ballistic missile technology, although it regularly fires short-range missiles into the sea off its east coast.

- US-China relations -

The two powers are likely to come head-to-head again at the Singapore meeting, where US Defence Secretary Ashton Carter is expected to make another tough speech that will anger China.

US officials have repeatedly accused China of fostering regional tensions in the South China Sea, but Beijing has accused Washington of militarising the area with its "freedom of navigation" patrols.

Carter has also lashed out at Chinese hacking of US companies' information systems ahead of his Singapore visit.

- Terrorism -

The rise of Islamist movements in Asia has seen hundreds of radicalised people from predominantly-Muslim countries like Indonesia, Malaysia and Bangladesh join terror groups such as the Islamic State.

IS even has an entire battalion comprising fighters from Southeast Asia, and governments have to grapple with returning fighters who have been fully trained in military tactics.