People gathered in the capital Dili and nearby areas, throwing stones and burning cars and houses, police say.
One person died and several others were injured, the police chief said.
The 7 July parliamentary election was seen as a key test on whether UN peacekeepers could leave by year-end.
Sandra McGuire, the UN mission’s communications chief in East Timor, said that they were not treating the violence as a major security incident.
“One of the interesting things is that the unrest was handled by the national police and handled well,” she told Radio Australia.
She added that the situation was under control and order had been restored.
East Timor gained independence from Indonesia in 2002 after three years of UN administration, which followed more than two decades of bloody guerrilla warfare during Indonesian rule.
UN peacekeepers arrived again in 2006 after widespread fighting and unrest. The UN says it will withdraw its peacekeepers if the parliamentary polls go smoothly, following peaceful presidential elections in April.