Energy firms led a sell-off in most Asian equity markets on Tuesday, a day after supply fears sent oil prices plunging, while confidence remains fragile owing to ongoing fears of a global trade war.

After hitting three-and-a-half-year highs at the start of the month, crude has dropped almost 10 percent as it is hit by a perfect storm of issues that have fuelled fears of a glut.

Worries about the impact on demand caused by a possible trade war between the US and China took their toll last week, as did news that Libya was exporting again after recent oil field closures.

That all came just weeks after major producers Saudi Arabia, Russia and OPEC agreed to lift a 2016 ceiling that had supported prices.

The latest spark for selling came Monday on reports the US may tap its Strategic Petroleum Reserve to lower prices, and speculation Riyadh was considering increasing output for some Asian countries.

Also Monday US Treasury Secretary Steven Mnuchin indicated the Trump administration could allow some exceptions to a ban on purchases of Iranian oil.

"It very much seems like a continued reaction to potential supply increases," Bart Melek, head of global commodity strategy at TD Securities in Toronto, told Bloomberg News.

"The combination of the supply-side effect and the potential for less demand as a result of trade woes that we're seeing are prompting people to take some of the long bets off oil right now."

Oil edged up slightly Tuesday but was unable to make inroads in the previous day's losses of more than four percent.