President Trump told Vietnamese President Tran Dai Quang on Friday that he wants to expand cooperation with the Southeast Asian nation on trade and regional issues.

Trump made the overture in a letter to Quang one week before he meets with Chinese President Xi Jinping, according to the Vietnamese government's website.

Trump's letter affirmed "his wishes to promote cooperation on economics, trade, regional and international issues," according to a statement.

There have been increased tensions between Vietnam and China over the South China Sea in recent years after China began building island fortresses there. Many of the small islands where China is building its installations are claimed by Vietnam, Taiwan, the Philippines, Malaysia and Brunei.

Trump said last week that he expects the meeting with President Xi to be a difficult one. South China Sea concerns are expected to come up, along with a host of trade issues.

On Friday, two military warships left California en route to the South China Sea for military exercises.