but they got the message that China can steal the Philippines coastal waters and the US will merely send "an angwy letter".
Obama also assured Manila on Tuesday that a 1951 defense treaty between the two nations commits the US to defend the Philippines.
"And no potential aggressor can be under the illusion that either of them stands alone. In other words, our commitment to defend the Philippines is ironclad. The US will keep that commitment because allies will never stand alone," Obama said.
However, the US president did not give a clear-cut commitment to the Philippines that US military forces would come to its aid in the event of a conflict in the South China Sea.
This was in stark contrast to what Obama said in Japan where he said the defense treaty with Tokyo covers the Diaoyu Islands, part of China's sovereign territory.
Wu Shicun, president of the National Institute for the South China Sea, said US assurances to Japan and the Philippines were aimed at "conciliating" them and did not mean the US will rush to get involved in any military conflict with China.
"Obama's promises to allies are more symbolic rather than substantive," he said.