Maritime nations met at the UN's International Maritime Organization (IMO) in London to enact a tax on shipping emissions that was rejected by the US and others, reported the Associated Press.

The proposed rules would introduce the first global tax on greenhouse gas emissions from ships, setting a marine fuel standard that tightens over time. Most vessels currently run on heavy fuel oil, a major source of carbon dioxide and pollutants.

US President Donald Trump urged countries to reject the plan, calling it a "global green new scam tax on shipping." Saudi Arabia, Russia and other nations also oppose the framework in its current form.

The Net-Zero Framework, agreed in principle in April, aims to cut shipping emissions to net-zero by around 2050. It includes incentives for using fuels with zero or near-zero emissions and imposes fees for exceeding emission limits.

Climate advocates say the framework is a historic opportunity. Emma Fenton of Opportunity Green called attempts to delay adoption "an affront to multilateralism." John Maggs of the Clean Shipping Coalition said failure to adopt the framework risks years of stagnation.

Shipping emissions now account for roughly three per cent of global totals. Observers say the outcome of the IMO meeting remains uncertain.