By CHRISTOPHER BODEENDANDONG, China (AP) â¿¿ North Korea's nuclear test Tuesday could push China to take a tougher stance against its longtime ally. Beijing had earlier signaled a growing unhappiness with Pyongyang by agreeing to tightened U.N. sanctions after North Korea launched a rocket in December, surprising China watchers with its unusually tough line, which prompted harsh criticism from Pyongyang. And while China isn't expected to abandon its communist neighbor, it appears to be reassessing ties a year after new North Korean leader Kim Jong Un took office. The question is for how long China, itself under new leader Xi Jinping, will continue to back North Korea's nettlesome policies. "Perhaps Kim Jong Un thinks Xi Jinping will indulge him. Perhaps he's in for a surprise," said Richard Bush, Director of the Center for Northeast Asian Policy Studies at the Brookings Institution in Washington D.C. However, the Foreign Ministry's initial statement was relatively mild and echoed almost word-for-word China's responses to North Korea's first two nuclear tests in 2006 and 2009. It said China expressed its "firm opposition" to the test, urged a calm response by all sides, and called for new denuclearization talks. China's state broadcaster reported on the earthquake that was the first indication that North Korea might have conducted a test. CCTV quoted residents living along the North Korean border in Jilin province as saying they felt the ground shaking for about one minute around the time the quake hit. North Korea later confirmed carrying out the test. China is feeling spurned by Kim. Although China welcomed his ascension after his father died in December 2011 and maintained flows of aid and investment, Kim has ignored China's interests in a stable neighborhood with his two rocket launches and nuclear test plan. North Korea announced last month it would conduct a test to protest the toughened U.N. sanctions.