Russian President Vladimir Putin again rejected US calls for new sanctions against North Korea after its sixth and most powerful nuclear test, echoing China's resistance to more punitive measures to pressure Pyongyang into abandoning its atomic and missile programmes.The Russian leader criticised sanctions as "useless and ineffective," instead urging the international community to offer security guarantees to North Korea. "They'll eat grass, but they won't abandon their programme unless they feel secure," he told reporters Tuesday at an emerging markets summit in Xiamen, China, which was hosted by his Chinese counterpart Xi Jinping.