BEIJING (AP) — China has towed a deep sea drilling rig to a spot off Vietnam's coast in waters claimed by both. The rig has been escorted by a reported 70 Chinese craft that have rammed Vietnamese ships and fended them off with water cannons, raising tensions between the nations to their highest in years.

Q: Why is China doing this? A: China claims virtually the entire South China Sea and has begun acting on announced plans to drill for what is thought to be a wealth of oil and natural gas beneath those waters. The moves may also be a test of Vietnam's ability and resolve to defend its own claims, along with Washington's insistence on freedom of navigation there.

Q: Where is the rig? A: China has placed its oil rig about 130 nautical miles off Vietnam's coast in waters already identified by Hanoi for exploration but not yet offered to foreign petroleum companies. Vietnam argues the territory is clearly within its continental shelf. China's argument is based on its historic claim to most of the South China Sea and on the rig's proximity to nearby Paracel Islands, which are also disputed.

Q: What are the legal arguments? A: China's move appears to go against the spirit of both U.N. conventions and agreements Beijing has with Southeast Asian nations that call for nations not to unilaterally engage in conduct that escalates disputes or jeopardizes a resolution to competing claims of sovereignty. The agreements, however, are hazy and unenforceable and China has ignored past commitments while rejecting calls for international mediation.

Q: What about the timing? A: China said the rig is a routine and logical outgrowth of a long-developing oil exploration program. However, its deployment follows a visit to the region by President Barack Obama during which he criticized China's moves to back its claims in the South China Sea and reaffirmed U.S. support for ally Japan in another territorial dispute in the East China Sea. Coming on top of U.S. plans to bulk-up its Asian presence, the remarks left China thoroughly displeased. It also comes ahead of this weekend's summit of the 10-nation Association of Southeast Asian Nations that includes both Vietnam and the Philippines, with whom China is also feuding over maritime claims. Beijing has been accused of meddling in the fragile grouping before, mainly to further its strategy of preventing the bloc from putting up a united front against China's territorial claims.

Q: What is China's end game? A: China's ultimate goal is to displace the United States as the region's dominant military power and draw its neighbors further into its economic and cultural orbit. Forceful measures to assert its South China Sea claims help build its clout, and there appears little likelihood of China backing away in the face of complaints, much less making concessions on territorial matters.

Q: What are Vietnam's options? A: Vietnam has significantly boosted spending on its military in recent years, but is heavily outgunned by China. While it has shown a willingness to fight China in the past, the economic stakes are higher now and it has little to gain from initiating a shooting war. Hanoi is trying to rally international support against China as an aggressor — charges that resonate with many in the region and the United States. But it lacks the solid alliance with the U.S that countries like Japan and the Philippines have as they confront China. It may now join Manila in perusing a legal challenge against China's sovereignty claims in an international tribunal, but it's unclear whether the prospect of this would be enough to persuade China to withdraw the rig.