European shares kicked off the second quarter on a subdued note, as investors were gripped by worries about economic growth and inflation, with Europe facing a deadline to start paying for Russian gas in roubles.

Russian President Vladimir Putin threatened to cut off gas supplies unless paid in local currency from April 1 - a move that could exacerbate an energy crunch in the continent as Russian gas imports account for about 40% of Europe's consumption.

The pan-European STOXX 600 index was flat at 0708 GMT as gains in sectors such as banks, healthcare and consumer staples were offset by a slide in technology and oil stocks.

Crude prices were hit after the United States announced the largest ever release from its strategic reserve and called on oil companies to increase drilling, hoping to control prices which at one point surged over 40% to $139 a barrel since Russia began an attack on Ukraine.

Negotiations aimed at ending the five-week war were set to resume even as Ukraine braced for further attacks in the south and east.

Among individual stocks, French catering and food services group Sodexo fell 5.5% on narrowing its full-year organic revenue growth forecast, citing uncertainties due to COVID-19 and the war in Ukraine.

(Reporting by Susan Mathew in Bengaluru; Editing by Anil D'Silva)