"This just shows that we need to have a strong navy," Ryan said at a news briefing. "We should not have a president proposing to lower our ship count to pre-World War One levels. This means we need to have a strong military and a strong Navy, and a real foreign policy, which we do not now have."
Ryan's comments came one day after China again landed a plane on a disputed island in the South China Sea. In addition to China, Vietnam, Malaysia, Brunei, the Philippines and Taiwan have rival claims to territory in those waters.
U.S. Republican presidential candidate and U.S. Senator Marco Rubio echoed Ryan's call, saying that, if elected, he would sail U.S. ships through the contested South China Sea to challenge China's claimed air and sea rights and work with other allies in the region.
"We need to reinvigorate our Pacific military alliance, and that begins with the United States investing the resources necessary to rebuild our Navy," Rubio told Fox Business Network.
Neither Ryan or Rubio said how much they would allocate in resources for the U.S. Navy.
Republicans, who are seeking to take control of the White House from Democrats in the November presidential election, have made U.S. President Barack Obama's foreign policy a key campaign issue.
The Obama administration has said it is concerned by the recent landings. The United States had not taken a stance on the competing claims, and the administration has repeatedly pressed for free, lawful navigation in the area.
"We again call for all claimants to reciprocally halt land reclamation, further development of new facilities, and militarization on their outposts and instead focus on reaching agreement on acceptable behaviour in disputed areas," State Department spokeswoman Anna Richey-Allen said.
Other top Republican lawmakers have previously criticized the Obama administration for not conducting more patrols in the South China Sea.
U.S. Navy officials have said the dispute could lead to a possible regional arms race.
Asked if he would intervene militarily to stop such Chinese plane landings if elected, Rubio said the United States needs to challenge China's claims.
"We should reject their sovereignty over these areas and we should continue to fly our airplanes over it and sail our ships though it," he said.