The pan-European Stoxx 600 slightly pared early losses but was still down 0.45% by the close. Travel & leisure , autos and chemicals baskets all fell more than 1% to lead losses as almost every sector traded in the red.

Market players are fleeing riskier assets like equities in favor of safer alternatives like gold and bonds after a U.S. airstrike last week killed Iran's top military commander, Qasem Soleimani, in Iraq. The attack has heightened already-volatile relations between Washington and Tehran.

Oil is also surging on the back of intensifying U.S.-Iran tensions, amid fears it could disrupt supply in the Middle East. Brent crude futures were up .6%, or 43 cents, at $68.60 a barrel at 4:30 p.m. London time. U.S. West Texas Intermediate (WTI) crude futures climbed 0.3%, or 17 cents, to $63.22.

Over the weekend, Iraq's parliament passed a resolution calling for the government to expel foreign troops from the country. President Donald Trump responded by threatening to impose sanctions on Iraq. Meanwhile, Iran has declared it will no longer adhere to uranium enrichment restrictions agreed under the 2015 nuclear deal.