Protests continued in China Monday after a weekend of violent demonstrations over Japan's purchase of a group of islands that both countries claim as their own. People gathered in front of the Japanese embassy-- it's walls stained with egg and vegetable juice from demonstrations a day earlier. Sunday Chinese protesters clashed with police-- burning Japanese flags and chanting anti-Japanese slogans. The protests were sparked after Japan announced last week it was buying a group of islands-- known as Senkaku in Japanese, and Diaoyu (dee-owe-you) in Mandarin-- from a private Japanese owner. Both countries are interested in the islands for their potentially valuable gas reserves. U.S. Secretary of Defense Leon Panetta, who is in Tokyo with Japanese defense ministers has urged both sides to remain calm. (SOUNDBITE) (English) U.S. SECRETARY OF DEFENSE LEON PANETTA SAYING: "Obviously ah we're concerned by the demonstrations and we're concerned by the conflict that is taking place over the Senkaku islands. And the message that I've tried to convey, is a message that we have to urge calm and restraint, on all sides." The U.S. has said they will not take an official position on matters of sovereignty-- although they are militarily aligned with Japan. Panetta will head to Beijing for more meetings later today.