President Barack Obama is on a four-nation, eight-day tour in Asia aimed at shoring up America's credibility with allies concerned about U.S. defense cutbacks while China moves to expand its power.
Asian countries such as Japan are nervous the United States won't help defend them if China tries to take some disputed islands by force.
But the president reassured Japanese officials it will stand with the island nation if its territory is threatened.
"Let me reiterate that our treaty commitment to Japan's security is absolute, and Article five covers all territories under Japan's administration, including the Senkaku islands," Obama said.
The president added, however, the United States will not take a position on whether the islands in the East China Sea belong to China or Japan, and the dispute will not lead him to draw a "red line" over military action.
Asian allies are concerned because they've watched Obama talk tough in Ukraine and Syria, but do very little.
The president said new sanctions against Russia are in the works for its actions in eastern Ukraine, adding that the United States needs support.
"We have been preparing for the prospect that we're going to have to engage in further sanctions," he said. "Those are teed up. It requires some technical work, and it also requires coordination with other countries."
But conservative critics suggest the president is weak on foreign policy.
"I think he's made a decision; he will not have a military conflict if he can at all help it," Dr. Paul Bonicelli, executive vice president of Regent University, told CBN News.
"And he's dealing with someone who knows that and is willing to push as far as he needs to to get everything that he wants, and so far Vladimir Putin is getting every single thing he wants," Bonicelli noted.
Lawmakers like Sen. John McCain, R-Ariz., agreed, describing the president's dealings with Russia as "disgraceful, and the rhetoric does not match the action."
America's Asian allies are also concerned about how the Obama administration has handled the Syria conflict.
"Certainly the issue of Syria really got to both Tokyo and Seoul because President Obama announced that he wanted to use military force, but that he first had to go to get Congressional approval," China expert Gordon Chang told CBN News.
"And that led many people in the region with defense treaties with the United States wondering whether if China attacked them, President Obama would have to go to Congress in order to honor our defense treaties," he said.