BEIJING (Reuters) -China urged calm and restraint on Tuesday after Iran said it had resumed 20% uranium enrichment at an underground nuclear facility, which breaches a 2015 nuclear pact with major powers, including China. The enrichment decision, Iran’s latest contravention of the accord, coincides with increasing tension between Iran and the United States in the last days of President Donald Trump’s administration. Iran started violating the accord in 2019 in a step-by-step response to Trump’s withdrawal from it the previous year and the reimposition of U.S. sanctions, which had been lifted under the deal. Chinese foreign ministry spokeswoman Hua Chunying said the Iran nuclear issue was at a critical juncture and was “extremely complex and sensitive”. “China urges all sides to exercise calm and restraint, to stick to the commitments of the agreement and to refrain from taking actions that might escalate tensions, so as to make space for diplomatic efforts and a change in the situation,” she told a daily news briefing in Beijing. “The urgent task at hand is for all sides to push the United States to return unconditionally to the agreement and remove all relevant sanctions,” Hua said. Doing so could help bring the agreement back onto “the right track”, she said. The agreement’s main aim was to extend the time Iran would need to produce enough fissile material for a nuclear bomb, if it chose to, to at least a year from roughly two to three months. It also lifted international sanctions against Iran. Iran insists it can quickly reverse its breaches if U.S. sanctions are removed. President-elect Joe Biden, who takes office on Jan. 20, has said the United States would rejoin the deal “if Iran resumes strict compliance” with it.