The pan-European STOXX 600 index was down 0.3% at 535.11 points, as of 07.12 GMT. Other major regional indexes also traded lower.
Iran and Israel exchanged air and missile strikes on Monday, as global tensions rose over Tehran’s expected response to a U.S. attack on its nuclear facilities over the weekend.
In a post to the Truth Social platform on Sunday, U.S. President Donald Trump questioned the possibility of regime change in Iran.
Markets fear that an Iranian retaliation may include a closure of the Strait of Hormuz, the world’s most important oil artery.
Bucking the sombre mood, the oil and gas sector led gains in the regional index, rising 0.7%, as oil prices jumped on fears of supply disruption following the weekend strike. Travel and leisure stocks lost 0.8%. Among stocks, Spectris rose 14.6% after private equity firm Advent said it will acquire the scientific instruments maker in a deal valued at 4.4 billion pounds ($5.91 billion).