Anti-government protesters have thrown Molotov cocktails and flares at riot police during a march through the Albanian capital, Tirana.
Thousands of demonstrators, many holding umbrellas, marched on May 13 in rain that at times mixed with clouds of white smoke from flares. Police officers did not respond.
"It is a march of protest against the illegitimate government," said Lulzim Basha, the leader of the main opposition center-right Democratic Party.
One police officer was reported injured in the unrest.
The opposition has been holding protests since mid-February, accusing government officials of corruption and of stealing votes in parliamentary elections two years ago.
They are demanding a transitional government and an early election.
The United States and EU lawmakers have called for calm after weekend protests turned violent.
A U.S. Embassy statement in Tirana on May 13 called on opposition leaders to condemn violence and "ensure that all future public protests are orderly and peaceful."
European parliamentarians also called on Albanians "to restrain from all forms of violence."
Albania expects to hear in June whether the EU will grant its request to launch full membership negotiations.