Vetra was leading 2-0 when hundreds of Legia Warsaw fans ran onto the field during the break, trying to tear down the goal nets and vandalizing billboards. The players and match officials had left the field.
Lithuanian TV pictures showed police in riot gear using tear gas to disperse the hooligans. One officer received minor injuries, and about 100 fans were arrested, Lithuanian police said.
The referee immediately abandoned the match. The teams never came back out on the field.
It was not immediately clear whether the result would stand or what UEFA's response was.