Europe's main stock index fell to a three-month low on Tuesday, as heightened geopolitical tensions following Russia's warning on its updated nuclear doctrine prompted investors to shift from risk assets to safe havens.

The pan-European STOXX 600 shed early gains to drop 0.9%, on track for a third straight day of loss, with safe-haven assets such as the gold and the U.S. dollar back on the rise.

The Kremlin said the aim of the updated nuclear doctrine was to make potential enemies understand the inevitability of Russian retaliation for an attack.

"I don't think this will have any impact on the (European) economy or earnings. It's just a natural reaction based on anytime the word nuclear is mentioned from any head of state," said Patrick Armstrong, chief investment officer at Plurimi Wealth.

"It obviously sets investors' minds about potential downside as well as an equity investment is driven by the hope for an upside. So I don't think it's anything other than rhetoric, and the market will just get past it."

Europe's fear gauge index surged to its highest level since earlier this month, signalling growing investor anxiety.

Automobiles and banks slumped around 2% each, the worst-hit sectors in an overall market decline.

The upcoming appointments for U.S. Treasury secretary and trade representative under President-elect Donald Trump is also in focus after last week's picks for health and defence roles.

Investors are starting to question the effect of Trump's inflationary policies like possible tax cuts, while also awaiting U.S. chip leader Nvidia's earnings on Wednesday, said Richard Hunter, head of markets, Interactive Investor.

With ECB policymakers expressing concern over potential U.S. trade tariffs hurting euro zone growth, any signals on the global interest rate-cut trajectory will be closely watched. Trump's policies are also seen as reigniting inflationary fears, complicating further U.S. rate cuts.

Among single stocks, Thyssenkrupp jumped 8% after releasing its fourth-quarter results, with a trader pointing to free cash flow a positive surprise.

Embracer rose 2% as Tabletop games publisher Asmodee is set to be spun off from the Swedish gaming group.

Swiss hearing aid maker Sonova Holding fell 2% following half-year core earnings miss.

Nestle reversed early gains to drop 1.3%. The food giant is set to boost advertising and marketing, trim costs by $2.8 billion by 2027 and carve out its water and premium drinks businesses into a standalone global unit.

Shares of Aeroports de Paris rose 3% after Stifel upgraded the French airport operator's stock to "buy" from "hold".

(Reporting by Ankika Biswas in Bengaluru and Joao Manuel Vicente Mauricio in Gdansk; Editing by Eileen Soreng and Sherry Jacob-Phillips)