GLASGOW, Nov 1 (Reuters) - Denmark, the United States and 12 other countries on Monday backed a goal to reduce emissions by the global maritime sector to zero by 2050, a target to be fleshed out in negotiations at the United Nations shipping agency. The initiative, led by Denmark and announced on the sidelines of the U.N. COP26 climate summit in Glasgow, Scotland, aims to build support among countries for the goal at the International Maritime Organization, which is considering new emissions-cutting measures by a 2023 deadline. "We urge the IMO to take action to set ambitious targets to achieve zero emission shipping by 2050," Danish Prime Minister Mette Frederiksen told a news conference at COP26. "Carbon-neutral shipping is vital to reaching our climate goals." Belgium, Britain, Finland, France, Germany, Honduras, Hungary, Iceland, the Marshall Islands, Norway, Panama and Sweden also signed the maritime sector declaration. It commits countries to "work at IMO to adopt such a goal, to adopt goals for 2030 and 2040 that place the sector on a pathway to full decarbonisation by 2050, and to adopt the measures to help achieve these goals". The IMO sets shipping regulations through its 175 member countries and aims to reach decisions through consensus. A tougher target would need approval from a majority, posing political challenges. Countries with big maritime shipping sectors including Japan and Greece did not sign the declaration. An IMO spokesperson said it would hold discussions on proposals from countries for broader climate measures to be adopted in 2023. "IMO is providing the global forum where member states can begin forward their proposals for discussion." In 2018 the IMO adopted an objective to halve international shipping emissions by 2050 from 2008 levels. That would still fall far short of the net zero CO2 emissions that scientists say the world must achieve by 2050 to avoid the most calamitous impacts of climate change. read more With around 90% of world trade transported by sea, global shipping accounts for nearly 3% of global CO2 emissions. Decarbonising the sector will require huge investments to scale up production of green fuels and launch clean ships this decade. The world"s largest container line, Denmark’s Maersk, plans to operate its first carbon-neutral ship in 2023 using green methanol produced from renewable sources. Some countries are pressing ahead with stricter policies. The 27-country European Union is considering a proposal to add shipping to the EU carbon market, forcing ship owners to pay a fee when they pollute. read more Britain is trying to assemble a group of countries to make a similar declaration on aviation at COP26, to push the U.N. aviation agency to set a tougher emissions target, according to documents seen by Reuters. read more