(Recasts with reported death of police officer, details)
ISTANBUL, March 13 (Reuters) - A protester in Istanbul died from a head injury and a police officer suffered a fatal heart attack during Turkey's worst day of civil unrest since anti-government protests swept the nation last summer, local media said late on Wednesday.
Riot police clashed with demonstrators in several Turkish cities on Wednesday as mourners buried a teenager, wounded in the protests last June, whose death this week after nine months in a coma sparked a fresh wave of disturbances.
A defiant Prime Minister Tayyip Erdogan, already battling a damaging corruption scandal weeks ahead of elections, cast the latest unrest as part of a plot against the state.
Police fired water cannon, tear gas and rubber pellets on a major Istanbul avenue to stop tens of thousands of protesters from reaching the central Taksim square. There were similar scenes in the centre of the capital Ankara and in the Aegean coastal city of Izmir.
Officers in riot gear chased pockets of protesters into side streets late into the night.
"There were two groups attacking the police and one youth suffered a head injury ... and lost his life," Aziz Babuscu, the ruling AK Party's Istanbul provincial head, told CNN Turk TV.
Hospital sources and local media in the eastern province of Tunceli, which also saw protests on Wednesday, said a police officer died after suffering a heart attack during the unrest.
The death on Tuesday of 15-year-old Berkin Elvan, who got caught up in street battles in Istanbul between police and protesters last June while going to buy bread for his family, has hit a raw nerve with many Turks.
Crowds chanting "Tayyip! Killer!" held up photos of Elvan earlier in the day as his coffin, draped in red and covered in flowers, was carried through the streets of Istanbul's working class Okmeydani district for burial.
Those attending the protests said Erdogan's silence on Elvan's death, in contrast to President Abdullah Gul and other public figures who issued messages of condolence, highlighted how out of touch he was with a large segment of Turkish society.
But the turbulent run-up to municipal elections on March 30 has shown little sign so far of seriously weakening Erdogan, whose AK Party dominates Turkey's electoral map and who remains fiercely popular in the conservative Anatolian heartlands after overseeing a decade of rising prosperity.
"Does democracy come with Molotov cocktails?," Erdogan told throngs of cheering supporters said at a campaign rally in the southeastern city of Siirt, weeks ahead of an election that is widely being seen as a referendum on his rule.
"The path of democracy is the ballot box. If you have the power, go to the ballot box," he said. (Reporting by Humeyra Pamuk and Ferit Demir in Tunceli; Writing by Nick Tattersall; Editing by Leslie Adler and Eric Walsh)