U.S. stocks fell anew Monday, halting a rally that lifted major indexes to their first week of gains this year.

The Dow Jones Industrial Average declined 208.29 points, or 1.3%, to 15885.22, with losses deepening in the last hour of trading.

Driving action yet again, U.S. crude oil prices slid 5.7% to $30.34 a barrel. Energy stocks led the...