U.S. Deputy Secretary of State Antony Blinken says China's massive land reclamation projects in the South China Sea and its increasing militarization of these outposts is fueling regional tension and raising serious questions about China's intentions.

Blinken made the comments in a speech to several hundred students at Vietnam's National University in Hanoi on Thursday.

He says the United States will defend its national interest and support its allies and partners in the region, and that it will continue to sail, fly, and operate anywhere that international laws allow.

His trip comes as a preparation for a visit by President Barack Obama to Hanoi in late May.