World trade ministers were locked in disagreement on fisheries subsidies, agriculture and digital customs duties as a major WTO conference was extended beyond its scheduled deadline and into Friday.

With no signs of a breakthrough on Thursday at the World Trade Organization's 13th ministerial conference (MC13) in Abu Dhabi, officials pushed back the formal closing session to 2:00 pm (1000 GMT) the following day.

"These negotiations are a bit like a roller coaster," said a source close to the talks.

The meeting in the capital of the United Arab Emirates opened on Monday with disagreements between the body's 164 member states on key issues that dominated the agenda of the talks.

They include fisheries subsidies, agriculture and a moratorium on customs duties for digital transactions.

"Ministers are working extremely hard and are making real progress," WTO spokesperson Ismaila Dieng said early Friday.

"However, the negotiations are difficult because of interlinkages between the areas under negotiation. Ministers will review texts overnight and will regroup early in the morning."

On Thursday, Indian trade minister Piyush Goyal told journalists that participants were "working with a very positive outlook to try to see what's the maximum we can get done", predicting "significant outcomes" on areas of concern to developing countries.

- Fisheries deal 'difficult' -

With farmer protests sweeping Europe and India, agriculture agreements have emerged as a particularly sensitive topic of debate.

Member states are trying to negotiate a text listing the subjects that merit further discussion.

Two draft texts are on the table, one more extensive than the other, according to sources close to the discussions.

India, which is keen on permanent rules governing public stockholding of food reserves, is pushing for a standalone food security deal at MC13.

But others, such as the United States and the European Union, are demanding a broader agriculture package.

Meanwhile, a new deal on fisheries was initially viewed as the most likely outcome of the MC13 talks.

But Goyal on Thursday said it was "very difficult to get a resolution".

After a 2022 deal that banned subsidies contributing to illegal, undeclared and unregulated fishing, the WTO hopes to conclude a second package focusing on subsidies that result in overcapacity and overfishing.

But there is little consensus on what constitutes small-scale artisanal fishing that would benefit from specific exemptions.

- E-commerce regulations -

Another sticking point is the extension of an e-commerce customs moratorium, which EU trade commissioner Valdis Dombrovskis on Thursday called "vital" to economic growth.

Since 1998, WTO members have agreed not to impose customs duties on electronic transactions. The moratorium has been extended at most ministerial meetings since then, but objections by India and other member states are now throwing it into jeopardy.

When asked if India would compromise on an extension, Goyal said: "Let's see what the others are budging on."

He warned, however, that an extension cannot be "taken for granted".

On Thursday, India, along with Brazil, once again threatened to block the moratorium's extension, according to several sources close to the talks.

Big questions also remain over how the MC13 will address the issue of dispute settlement reform -- a main point of contention between the US and India.

Washington, under former President Donald Trump, brought the dispute settlement system to a grinding halt in 2019 by blocking the appointment of new judges to the WTO's appeals court, its highest dispute settlement authority.

During the last WTO ministerial in 2022, member states reached a commitment to having a fully functioning dispute settlement system in place by 2024.

"What we're going to see, I think, is a quite succinct (MC13) declaration which is not going to sort out the substance," said a Western diplomatic source who asked not to be named.

"It will recognise the progress we have made and that there is more work to be done, and that we have committed ourselves to get the system up and running in the course of this year."