Kuala Lumpur, Malaysia – As toxic haze from Indonesia’s worst wildfires in a decade clouded skies across Malaysia and Singapore over the past two months, a growing clamour of voices has demanded legal accountability.

In theory, a patchwork of domestic and international laws makes it possible for Southeast Asian governments to hold polluters responsible for cross-border haze, most of which has been blamed on land clearing by Indonesian palm oil plantation owners.

In practice, sensitivities around national sovereignty, a lack of enforcement mechanisms, and the practical challenges of evidence collection make legal action difficult, if not infeasible.

On paper, Southeast Asian countries are committed to working together to prevent cross-border air pollution under the ASEAN Agreement on Transboundary Haze Pollution, signed in 2002.

The legally binding treaty commits the 11 members of the Association of Southeast Asian Nations (ASEAN) to tackle haze, a recurring issue for decades, through “concerted national efforts and intensified regional and international co-operation”.

However, the agreement does not contain provisions for enforcement by a judicial body such as the International Court of Justice, which requires all parties to consent to its jurisdiction, and disagreements over interpretation and application can only be settled through negotiation.

Implementation of the treaty has also moved at a snail’s pace.

The treaty’s coordinating office, located in the Indonesian capital, Jakarta, only opened this April, nearly a quarter-century after it was envisioned.

“For decades, the response to haze has largely focused on diplomatic engagement, emergency firefighting, and measures to protect public health,” Heng Kiah Chun, a regional campaign strategist for Greenpeace Southeast Asia, told Al Jazeera.

“While these efforts are necessary, they have not sufficiently addressed the underlying causes, including forest and peatland destruction, unsustainable land-use practices and inadequate corporate accountability,” Chun said.

Malaysia and Singapore, where haze has propelled major population centres to the top of global tables for poor air quality, have refrained from criticising Indonesia, instead offering assistance to fight the fires, which are estimated to have burned more than 2 million hectares (about 5 million acres) of land in the archipelago.

Jakarta has given mixed signals on accepting outside assistance, with officials vacillating between welcoming the offers and insisting they can handle the fires themselves.

Mohd Hazmi Mohd Rusli, an associate professor and legal expert at Universiti Sains Islam Malaysia, said Southeast Asia’s long-standing emphasis on consensus and noninterference has hampered action.

“Economic interests and diplomatic considerations also play a role,” Rusli told Al Jazeera.

“Malaysia and Singapore have traditionally favoured diplomatic engagement over direct confrontation in managing sensitive bilateral and regional issues, reflecting ASEAN’s broader preference for consultation and consensus.”

Rather than negotiate new legal frameworks, ASEAN should strengthen its existing treaty “through independent monitoring, clearer compliance procedures, greater corporate accountability and stronger domestic enforcement”, Rusli added.

With diplomatic efforts having little impact, attention has increasingly turned to the possibility of countries using domestic laws with extraterritorial reach, an approach pioneered by Singapore.

Under the 2014 Transboundary Haze Pollution Act, Singaporean authorities are empowered to prosecute polluters for activities taking place overseas, with violators liable for fines of 100,000 Singapore dollars ($78,300) a day up to a maximum of 2 million Singapore dollars ($1.56m).

The act also enables the city-state’s National Environment Agency to issue notices directing companies to cease burning on their lands.

The agency has issued such notices to 10 Indonesia-based firms during this year’s wildfire season. But to date, no company has actually been prosecuted under the Singaporean law.

While the legislation allows authorities to identify suspected polluters through meteorological data, satellite imagery, and maps, prosecutors would likely struggle to establish guilt beyond a reasonable doubt in any case without firsthand evidence from Indonesia.

“Such direct evidence can only be obtained if the Indonesian authorities themselves investigate and take action against these very companies and share their evidence with Singapore,” Alan Khee-Jin Tan, an expert in environmental law at the National University of Singapore (NUS) Faculty of Law, told Al Jazeera.

“The most likely ‘defence’ the companies will take is that the fires started outside their concessions and spread into their holdings.”

Malaysia’s government has said it could consider legislation similar to the Singaporean law, but cautioned that implementation would be difficult.

In 2023, the government abandoned proposals for a law against cross-border haze, citing the difficulty of obtaining evidence for prosecution.

In 2016, Singapore and Indonesia became embroiled in a diplomatic dispute after the city-state’s environmental agency attempted to summon the director of an Indonesian company linked to the haze for questioning.

Indonesia’s then environmental minister, Siti Nurbaya Bakar, accused Singapore of not showing “mutual respect”, a suggestion denied by officials in the city-state.

On Wednesday, Indonesian President Prabowo Subianto hit out at countries that “like to insult” his nation over the fires, while pledging to expose foreign companies that he claimed were also responsible for the crisis.

Prabowo said his government took the issue seriously, with authorities arresting individuals found to have started fires, but it would “step up our response”.

The Indonesian leader’s remarks came after a Malaysian politician last week said that Indonesia should be treated as an “outcast” within ASEAN over the haze.

NUS law expert Tan said that while Singaporean authorities could launch a test-case prosecution against Indonesian companies without Jakarta’s assistance, they are unlikely to do so unless Indonesian authorities act first.

“Practically, they are likely to proceed only against those companies which the Indonesian authorities have themselves clearly identified and charged as perpetrators,” he said, adding that a failed prosecution could also expose the legislation as toothless.

“Otherwise, any action that Singapore takes would appear to the Indonesians to be unilateral, and could be politically controversial.”

Eugene Tan Kheng Boon, an associate professor of law at Singapore Management University, said Indonesia’s failure to take stronger action was the ultimate stumbling block to a resolution, but countries could also strengthen their own laws and regulations.

“This could include requiring commodities such as palm oil sold in the region and used in other products to be certified to be sustainably sourced,” Tan told Al Jazeera.

“Customers in the region can also boycott purchasing items from companies that are responsible for the haze,” he said.

“Banks that finance these polluters should also come within the enforcement crosshairs.”

Matthew Baird, director of the Asian Research Institute for Environmental Law, said that stronger political will in the region was needed above all else.

“Governments really have to sit together and work on really good strategic options, like the Chinese government did for air pollution in Beijing, where they were able to reduce air pollution – but it took 30 years and a lot of money,” Baird told Al Jazeera.

“Governments in Southeast Asia have to do it, and they have to get companies to change their behaviour, and that takes time, effort, and probably a lot of litigation,” Baird.

This would involve “holding directors to account, sending directors to jail, holding companies to account, and making sure that they fulfil obligations”, he added.

“Because in every country, it is actually a criminal offence to burn land.”