U.S. says time to act on North Korea, China says not up to Beijing alone

By Michelle Nichols and Lesley WroughtonUNITED NATIONS (Reuters) - U.S. Secretary of State Rex Tillerson warned on Friday that failure to curb North Korea's nuclear and ballistic missile programs could lead to 'catastrophic consequences,' while China and Russia rebuked Washington's threat of military force.The showdown in a meeting of the U.N. Security Council on North Korea highlighted the diplomatic challenges of resolving tensions over Pyongyang, with the Trump administration aggressively pre