UNITED NATIONS (Reuters) - Germany accused Russia and China on Tuesday of preventing a United Nations Security Council committee from determining whether North Korea has breached a U.N. cap on refined petroleum imports by the isolated Asian state.The Security Council has ratcheted up sanctions on North Korea since 2006 in a bid to choke funding for Pyongyang’s nuclear and ballistic missile programs. In 2017 it imposed an annual cap of 500,000 barrels on refined petroleum imports. China and Russia are the only countries to have notified the Security Council’s North Korea sanctions committee of refined petroleum exports to Pyongyang, but they did so in tonnes instead of barrels and the committee has been unable to agree on a conversion rate so it can determine when the cap was reached. “Despite numerous attempts - the issue has been on the agenda for no less than three years - to find an agreement on a conversion rate, Russia and China have been stalling the process,” German U.N. Ambassador Christoph Heusgen, chairman of the sanctions committee, told reporters. “While this shouldn’t be a complicated matter to solve, it has become clear that the two delegations are politicizing this topic,” Heusgen said, after raising the issue behind closed doors in a formal Security Council meeting. The Russian mission to the United Nations did not immediately respond to a request for comment. A spokesperson for China’s U.N. mission said the U.N. resolution imposing the refined petroleum cap does not specify what unit of measurement should be used and that negotiations on a conversion rate involve “complicated technical issues” and “it’s normal that relevant parties have differences.”