* PM's criticism of dead boy, family may stir tensions
* Boy's death sparked anti-government protests in Turkey
* President Gul urges calm before local elections (Adds Gul, Saturday's rally, more recordings leaked)
By Seda Sezer
ISTANBUL, March 15 (Reuters) - Turkish Prime Minister Tayyip Erdogan said a teenager who died this week after sustaining a head injury in anti-government protests last summer was linked to "terrorist organisations", in comments likely to fan political tensions.
The death of 15-year-old Berkin Elvan on Tuesday after nine months in a coma sparked Turkey's worst unrest since nationwide anti-government demonstrations last June, compounding Erdogan's woes as he battles a graft scandal that has become one of the biggest challenges of his decade in power.
Erdogan made his remarks, his first about Elvan, late on Friday at a campaign rally in southeast Turkey ahead of nationwide municipal elections on March 30.
"This kid with steel marbles in his pockets, with a slingshot in his hand, his face covered with a scarf, who had been taken up into terrorist organisations, was unfortunately subjected to pepper gas," Erdogan told a crowd of supporters in a speech broadcast on state-run TRT-Haber news channel.
Elvan, then 14, got caught up in street battles in Istanbul on June 16 while going to buy bread for his family. He was hit in the head by what is believed to be a police gas canister, slipped into a coma and became a rallying point for government opponents, who held regular vigils at the hospital where he lay in intensive care.
After his death, riot police used water cannon, tear gas and rubber pellets to disperse tens of thousands of protesters who took to the streets of Turkey's largest cities chanting "Tayyip! Killer!" and "Everywhere is Berkin, everywhere is resistance."
At campaign rallies, Erdogan has accused a coalition of "anarchists, terrorists and vandals" as well as opposition parties and an influential U.S.-based Islamic cleric, Fethullah Gulen, of orchestrating the unrest to undermine him.
Using harsh words unlikely to soothe public anger, Erdogan - who unlike President Abdullah Gul and other public figures did not send condolences to Elvan's family - criticised the boy's parents and suggested he had not really gone to buy bread.
"His mother says 'my son's killer is the prime minister'. I know love, fondness for one's child, but I could not understand why you threw steel marbles and carnations into your son's grave," Erdogan said at his election campaign rally.
Elvan's family are Alevis, a religious minority in mainly Sunni Muslim Turkey which espouses a liberal version of Islam and has often been at odds with the Islamist-rooted government.
In a tone contrasting sharply with Erdogan's fiery rhetoric, Gul called on Saturday for calm ahead of the local elections.
"Our people will go to the ballot box soon. It's everybody's duty to avoid moves, comments and behaviour which could raise tension in this critical process and to use common sense," Gul, a political ally of Erdogan, told the Hurriyet newspaper.
At a rally in Adana province in southeast Turkey on Saturday, Erdogan again complained that the Gulen movement - which has many followers in Turkey's police and judiciary - was behind the corruption scandal now dogging his government.
"With the guidance of the organisation's head in Pennsylvania, dirty games were staged in Turkey. While this was happening ... we continued serving this country," he said.
Gulenists are widely believed to be behind a series of leaked audio recordings purportedly exposing graft and other malpractices in Erdogan's inner circle. Gulen denies any involvement in the scandal.
Erdogan says the recordings are fabricated "montages" of conversations. More voice recordings were leaked overnight.
Erdogan, who has presided over a decade of rising living standards, remains Turkey's most popular politician and his AK Party is expected to outstrip its rivals in the local polls.
But critics say the prime minister is becoming increasingly authoritarian and intolerant, pointing to moves to tighten government control of the judiciary and of the Internet.
Erdogan says the moves are necessary to counter what he sees as attempts by Gulen, a former ally-turned-foe, to smear him and his government and to undermine him before the elections. (Editing by Gareth Jones)