Asian energy firms retreated Tuesday after a plunge in oil prices, while the pound's troubles mounted on worries about Britain's plans to leave the European Union.

Both main crude contracts sank almost four percent on Monday as traders fret over Iraq's commitment to stick to output cuts agreed amid much fanfare by OPEC and other key producers in November.

The deal sent the cost of a barrel surging last month towards $60 on hopes the cuts could reduce a global glut that had sent prices to near 13-year lows last February.

However, Iraq’s oil minister said exports from its southern ports reached a record high in December, leading to suspicion it will not stick to the cuts, which came into effect on January 1.

"The Iraqi headlines have raised concerns about compliance," John Kilduff, a partner at New York-based hedge fund Again Capital LLC, told Bloomberg News. 

"We need to see compliance outside of Saudi Arabia, Kuwait and the other Gulf states."

While both contracts edged up Tuesday, regional energy firms fell although they pared early losses. Sydney-listed Woodside Petroleum lost 0.1 percent and BHP Billiton was down 0.4 percent.

Inpex lost 1.5 percent in Tokyo and CNOOC was down 1.3 percent in Hong Kong. PetroChina was flat.

- Brexit apprehension -

Among regional markets Tokyo and Sydney each ended down 0.8 percent and Seoul shed 0.2 percent. There were also losses in Mumbai and Kuala Lumpur.

Shanghai closed down 0.3 percent but Hong Kong added 0.8 percent, with investors welcoming data showing China's factory-gate prices rose last month at their fastest pace in more than five years.

In early European trade London added 0.3 percent, having closed Monday at a record high, Frankfurt gained 0.2 percent and Paris put on 0.1 percent.

On currency markets the pound struggled at three-month lows against the dollar after British Prime Minister Theresa May said at the weekend the country would have control over its borders after Brexit -- suggesting she would be prepared to quit Europe's single market to achieve it.

"The Brexit narrative has also contributed to market apprehension and added to souring global risk sentiment," said Stephen Innes, senior trader at OANDA.

That unease has filtered through to other parts of the currency market, with the yen extending gains against the dollar. Analysts say there are fears the greenback's rally since Donald Trump's election may have been overdone.

Investors "were keen to take shelter under the yen's umbrella while Brexit cloud storms build", Innes added.

- Key figures around 0800 GMT -

Tokyo - Nikkei 225: DOWN 0.8 percent at 19,301.44 (close)

Shanghai - Composite: DOWN 0.3 percent at 3,161.67 (close)

Hong Kong - Hang Seng: UP 0.8 percent at 22,744.85 (close)

London - FTSE 100: UP 0.3 percent at 7,257.02

Pound/dollar: DOWN at $1.2150 from $1.2158  

Euro/dollar: UP at $1.0599 from $1.0574 

Dollar/yen: DOWN at 115.70 yen from 116.07 yen 

Oil - West Texas Intermediate: FLAT at $51.96 per barrel

Oil - Brent North Sea: FLAT at $54.94 per barrel

New York - Dow: DOWN 0.4 percent at 19,887.38 (close)

Source: AFP