A Republican senator is blocking the appointment of a top Pentagon official on Asia policy in a dispute with President Barack Obama over sales of fighter jets to Taiwan.

The Obama administration has approved upgrades for Taiwan's existing fleet of F-16s but not the sales of new planes that Sen. John Cornyn and other lawmakers want.

Spokesman Drew Brandewie said Cornyn wants a clear plan to address Taiwan's "shortfall" in fighter jets before he lifts his hold on the nomination of former Obama aide Mark Lippert to be assistant secretary of defense for Asian and Pacific security affairs.

The administration wrote to Cornyn last week saying the F-16 upgrade meets Taiwan's current needs although it cannot match China's much bigger air force "one-for-one."