White House deputy national security adviser Ben Rhodes, speaking to reporters after the two leaders met on the eve of a nuclear security summit in Seoul, said Washington and Ankara were open to considering further "non-lethal" aid for the Syrian opposition at a "Friends of Syria" meeting in Turkey on April 1.

"We worked on a common agenda in terms of how we can support both humanitarian efforts (and) the efforts of Koffi Annan to bring about much needed change (in Syria)," Obama said after his meeting with Erdogan, a sharp critic of Syrian President Bashar al-Assad.