It touched nearly 795 metric tonnes in 2022, nearly double the production in 2021 - 423 metric tonnes - the year of the military coup.

The UN believes this is driven by economic hardship and insecurity, along with higher global prices for the opium resin that is used to make heroin.

The coup plunged much of Myanmar into a bloody civil war that still continues.

"Economic, security and governance disruptions that followed the military takeover of February 2021 have converged, and farmers in remote, often conflict-prone areas in northern Shan and border states, have had little option but to move back to opium," said Jeremy Douglas, the regional representative for the UN Office on Drugs and Crime (UNODC).

The region, where the borders of Myanmar, Thailand, and Laos meet - the so-called Golden Triangle - has historically been a major source of opium and heroin production.

The UN report released on Thursday said Myanmar's economy was confronted by external and domestic shocks in 2022 - such as the Russia-Ukraine war, continued political instability and soaring inflation - which provide "strong incentives" for farmers to take up or expand opium poppy cultivation.

Myanmar is the world's second-largest producer of opium, after Afghanistan. The two countries are the source of most of the heroin sold around the world. Myanmar's opium economy is valued at up to $2bn (£1.6bn), based on UN estimates, while the regional heroin trade is valued at approximately $10bn.

But over the past decade crop substitution projects and improving economic opportunities in Myanmar have led to a steady fall in cultivation of the opium poppy.

The annual opium survey conducted by the UN, however, shows that production in Myanmar has risen again. Opium production in 2022 has been the highest since 2013, when the figure stood at 870 metric tonnes.

Since the coup the UN has also monitored even larger increases in synthetic drug production. In recent years, this has supplanted opium as the source of funding for armed groups operating in the war-torn border areas of Myanmar.

However, opium requires a lot more labour than synthetic drugs, making it an attractive cash crop in a country where the post-coup economic crisis has dried up many alternative sources of employment.

Opium farmers' earnings grew last year to $280/kg, a sign of the attractiveness of opium as a crop and commodity, as well as strong demand. It is a key source of many narcotics, such as heroin, morphine and codeine.

Opium poppy cultivation areas in 2022 rose by a third to 40,100 hectares, according to the report, which also pointed to increasingly sophisticated farming practices. Average opium yields have also risen to the highest value since the UNODC started tracking the metric in 2002.

Mr Douglas said Myanmar's neighbours should assess and address the situation: "They will need to consider some difficult options."

He added that these solutions should account for the challenges people in traditional opium-cultivating areas face, including isolation and conflict.

"At the end of the day, opium cultivation is really about economics, and it cannot be resolved by destroying crops which only escalates vulnerabilities," said Benedikt Hofmann, UNODC's country manager for Myanmar.

He added: "Without alternatives and economic stability, it is likely that opium cultivation and production will continue to expand."

According to an earlier UNODC report, prices for opium soared in Afghanistan last spring after the ruling Taliban announced a ban on cultivation.