BRUSSELS (Reuters) - NATO urged all countries to step up efforts to enforce sanctions on North Korea and stop its weapons tests - an appeal that diplomats said was aimed at the reclusive state s trading partners, suspected of holding back on penalties. All 29 ambassadors of the U.S.-led military alliance issued the statement as world powers sought a common response to North Korea s sixth and largest nuclear bomb test, amid fears that more were on their way.  It is now imperative that all nations implement more thoroughly and transparently existing UN sanctions and make further efforts to apply decisive pressure to convince the DPRK regime to abandon its current threatening and destabilizing path,  the statement read, referring to North Korea s official name, the Democratic People s Republic of Korea.  Diplomats, speaking on condition of anonymity, said there were concerns that existing sanctions on North Korea have not been fully enforced by Pyongyang s few remaining trading partners, namely China and several African nations.  China, African, other Asian countries continue to trade with North Korea. Our governments are saying to Guinea-Bissau, to Malaysia, to China that they need to tighten their sanctions enforcement,  said a NATO diplomat involved in discussions about how to resolve the North Korea crisis.  Efforts to impose fresh sanctions on Pyongyang at the United Nations have run into opposition.  President Vladimir Putin has resisted restrictions on oil exports to the country, saying the crisis will not be resolved by sanctions. NATO is not directly involved in the nuclear crisis, but it has repeatedly called on North Korea to abandon its nuclear and ballistic missile programs. NATO Secretary-General Jens Stoltenberg said separately he planned to travel to South Korea and Japan in October 