Most Asian markets slipped Thursday, with energy shares hit by a plunge in oil prices, while investors await Britain's election result and testimony from fired FBI boss James Comey on his probe into the Trump administration's Russia links.

Traders are on tenterhooks ahead of the big events, which could either fuel a sharp sell-off or reignite a rally that has seen some indexes hit multi-year -- and even all-time -- highs in recent weeks.

Crude prices sank more than five percent Wednesday after data showed an unexpected rise in US stockpiles, including gasoline, a particularly troubling sign for demand as the country's summer driving season kicks in.

The reading overshadowed an agreement last month by OPEC and Russia to extend a production cut in order to address an ongoing supply glut that is weighing on prices.

“Any chat of more OPEC cuts is likely to fall on deaf ears should they be made because the point of the cuts is to lead to a supply deficit,” said Greg McKenna, chief market strategist at AxiTrader.

While both main contracts edged up in Asian trade, energy firms were still feeling the effects of Thursday's slide.

Woodside Petroleum fell two percent in Sydney while Hong Kong-listed CNOOC shed 0.7 percent. Inpex was down 0.6 percent in Tokyo.

The main focus is on Comey's evidence to a congressional committee, which could be damaging to Trump.

In written testimony released Wednesday, Comey said the tycoon urged him to drop a probe into former national security advisor Michael Flynn and his contacts with Russia, confirming news reports.

- 'Smoking gun' -

US stocks did not react to the testimony, which also expressed the fired FBI chief's profound discomfort with Trump's behaviour.

However, US markets were unfazed by the letter, which Stephen Innes, senior trader at OANDA, said "offered no smoking gun or impeachment-worthy bombshells and only repeated what the market had already known".

In Asian trade Tokyo ended the morning 0.1 percent higher with dealers brushing off news that the Japanese economy grew at a slower rate than first thought in January-March.

But Hong Kong lost 0.1 percent and Sydney gave up 0.2 percent while Seoul was off 0.4 percent. Shanghai eased 0.1 percent ahead of the release of Chinese trade data later in the day. Singapore and Wellington also dipped.

In Britain Prime, Minister Theresa May's Conservatives are expected to win the national vote, but their once commanding lead in opinion polls has been slashed since she called it, leading to fears of political uncertainty ahead of key Brexit talks.

However, the pound remains buoyant on expectations of a Conservative win, with analysts predicting it could jump to $1.32 if May wins a comfortable majority. It is currently at $1.2961.

The euro was struggling on speculation the European Central Bank would lower its eurozone inflation forecasts through to 2019, leading to worries it would stick to its loose monetary policy.

The single currency had been rallying on hopes the lender, which holds a meeting Thursday, would begin to tighten monetary policy as the bloc's economy picks up.

- Key figures around 0230 GMT - 

Tokyo - Nikkei 225: UP 0.1 percent at 19,993.97 (break) 

Hong Kong - Hang Seng: DOWN 0.1 percent at 25,960.31

Shanghai - Composite: DOWN 0.1 percent at 3,136.93

Pound/dollar: UP at $1.2961 from $1.2959 at 2100 GMT

Euro/dollar: DOWN at $1.1252 from $1.1266 

Dollar/yen: UP at 109.88 from $109.81 yen

Oil - West Texas Intermediate: UP 28 cents at $46.00 per barrel

Oil - Brent North Sea: UP 32 cents at $48.38 per barrel

New York - Dow: DOWN 0.2 percent at 21,173.69 (close)

London - FTSE 100: DOWN 0.6 percent at 7,478.68 (close)