Six years after one of the world's most devastating factory disasters led to international safety monitoring in Bangladesh, campaigners are warning of "grim consequences" if such oversight is abandoned.

The collapse of the nine-floor rabbit warren of textile factories at Rana Plaza in Dhaka on April 24, 2013 killed 1,138 workers and shone a spotlight on the poor safety standards in Bangladesh's $31 billion garment industry.

Under intense pressure, top brands such as H&M, Inditex, Carrefour and Gap set up two watchdogs to look at more than 4,500 factories that make clothes for Western stores.

One of the watchdogs, the Alliance for Bangladesh Worker Safety, has already wrapped up after reviewing nearly 1,000 factories that produced mostly for US brands.

The future of the larger monitor, "Accord on Fire and Building safety", representing some 200 European labels such as H&M, Primark and Tesco, is to be decided by Bangladesh's Supreme Court after a lower court ruled it should also wind up.

Laura Gutierrez of the US-based Worker Rights Consortium, a labour group, warned that ending the international oversight "will have grim consequences for workers and factory owners".

It "will cause brands to see the country as a far riskier place to produce," she added.

Christie Miedema of the Clean Clothes Campaign added that progress of safety "will be lost –- setting the country on a path back to the situation before the Rana Plaza collapse".

Top brands including H&M, Zara, Adidas, Tesco and Next have backed concerns raised by such labour rights groups.

British brand Next said that "any early termination of the current Accord operations in Bangladesh would be detrimental to the safety of workers in the readymade garment industry there".

Accord, for its part, says it needs more time to enforce safety in the 1,700 factories it has reviewed so far, while manufacturers argue that the programme's five-year mandate has already expired.

- Major fires -

The Bangladesh government says factory fatalities have dramatically declined since the disaster because of upgrades overseen by the monitoring groups and local agencies.

It argues that the national inspection agency can now handle the enforcement of factory safety alone.

However, two major fires in Dhaka -- in which 100 people died -- have highlighted the lingering dangers.

One of those blazes tore through a 22-storey building that housed several garment businesses. A probe found it did not have a safety license and breached multiple construction rules. Many emergency exits were locked.

Despite this, the influential Bangladesh Garment Manufacturers and Exporters Association (BGMEA), whose members own the factories, want international oversight to end.

The group's outgoing President Siddiqur Rahman told AFP it is "negotiating for an amicable settlement with the Accord steering committee".

- 'Shocking level of unreadiness' -

Campaigners say that textile companies fear the monitors could start looking into other workers' rights issues, in an industry where minimum wages start at $95 dollars a month.

"Manufacturers fear Accord might put the industry under greater scrutiny," said Salahuddin Swapan, a Bangladesh garment union leader.

Critics say that Bangladesh's factory inspection agency, which would take over the monitors' work, lacks the means and desire to push through costly safety upgrades.

But Shib Nath Roy, head of the Department of Inspection for Factories and Establishments (DIFE), said the agency was now better placed than the international monitors to take on the work.

He said it had had "made significant progress" with scores of extra inspectors employed since the Rana Plaza disaster.

A consortium of groups campaigning for garment workers' rights, including the Clean Clothes Campaign and International Labour Rights Forum, dispute that the government is ready to take over.

They say none of the 745 factories under the government inspection programme has yet eliminated "high risk safety hazards" identified in the past five years.

"Our research shows a shocking level of unreadiness" by the government to take over Accord's work, they said in a report this month.