* Polls last step of transition to democracy after 2012 coup
* Key to unlocking billions of dollars in development aid
By Tiemoko Diallo and Adama Diarra
BAMAKO, Dec 15 (Reuters) - Voters in Mali headed to the polls on Sunday but turnout was low for a second round of legislative elections meant to complete democratic transition after a coup last year led to an Islamist takeover of the north.
A French-led military intervention in January drove al Qaeda-linked fighters from northern towns, and Malians elected President Ibrahim Boubacar Keita in an August runoff.
Completion of the parliamentary vote should unlock $3.25 billion pledged by donors to rebuild the impoverished country and develop its lawless desert north.
The first round last month was marred by abuses, however, including ballot box theft, though observers later said the incidents had no effect on the outcome.
No such violence was reported during Sunday's vote but turnout remained poor, with many polling stations seeing only a trickle of voters.
"I've just gone around to visit polling stations and I'll admit that I'm worried by this situation," said Aliou Dao, who voted in the riverside capital Bamako. "What has happened that's made Malians refuse to vote?"
Turnout for the November vote was just 38.5 percent, against the record 49 percent of 6.8 million registered voters who cast ballots in the first round of the presidential election in July.
"The ballot counting will start now," Lassana Coulibaly, an election worker at a polling station in Bamako's Banankabougou neighbourhood, said soon after voting ended at 6 p.m. (1800 GMT). "For us it will be quick, since we only had 82 voters."
The majority of the 147 seats in parliament remained up for grabs on Sunday after candidates won just 20 decisive victories in the first round last month.
"From what I've observed it's within the norms. It's going well," Louis Michel, the head of the European Union's observer mission, told state television.
"Obviously it's good when participation is high, but what's important is that voters were able to vote," he said.
Despite some discontent in southern Mali with his peace overtures to northern Tuareg separatist rebels, Keita's RPM party is expected to win the election. Universally known by his initials IBK, Keita swept the Aug. 11 presidential runoff with 78 percent of the vote.
While France's massive military operation earlier this year pushed the Islamists out of major population centres, isolated cells have remained active and Mali has suffered a surge in Islamist violence since Keita was elected.
A suicide bomber killed two Senegalese U.N. peacekeepers and destroyed the only operating bank in the northern Malian town of Kidal on Saturday.
Voters in the Tuareg rebel stronghold elected their representatives in the first round and there was no voting there on Sunday.
France has more than 2,000 troops stationed in Mali but aims to reduce its military presence to 1,000 by February as it hands security responsibilities to the Malian army and the U.N. force. The U.N. mission, launched in July, is still at roughly half its 12,600-man planned strength. (Writing by Joe Bavier; Editing by Sonya Hepinstall)