By Jonny Hogg and Gulsen Solaker
ANKARA, March 20 (Reuters) - The anger, threats and conspiracy theories in Turkey's election campaign have prompted both sides to warn about ballot abuse, with the main opposition saying it alone plans to deploy half a million poll observers.
Prime Minister Tayyip Erdogan's embattled ruling AK Party is expected to follow suit, with at least one of its prominent candidates warning of "vanishing ink" on ballots.
Erdogan, in office for 11 years, was rocked by anti-government protests last June, rekindled in recent weeks, and is now dealing with a corruption scandal swirling around his inner circle, something he says is orchestrated by opponents.
Polls suggest his party is on course to maintain its dominance of the electoral map in the March 30 municipal vote. But there is an increasingly polarised political landscape, tight races in the major cities of Istanbul and Ankara, and a building concern about fraud.
"When we take into account the atmosphere in Turkey right now, this election is more meaningful than ever," said Emrehan Halici, deputy chairman of the main CHP opposition party.
He said the CHP would deploy 500,000 people to monitor voting at all 200,000 ballot boxes across the country and bolster an online system it launched at general elections in 2011 to allow voters to cross check the results.
"Turkish citizens have doubts over these elections, and they're right to," Halici told Reuters.
The local elections mark the start of a critical 15-month voting cycle for Turkey, with presidential and parliamentary polls also due, and the campaigns on both sides have been peppered with allegations of potential fraud.
It was the AK Party mayoral candidate in Ankara who this week warned about the risk of "vanishing ink". Erdogan himself has told rallies of his supporters not to be duped by opponents using social media to try to trick them into inadvertently spoiling their ballots.
"ATMOSPHERE OF MISTRUST"
Despite a turbulent political past, Turkey's previous elections have been largely seen as free and fair, with overall control of the process resting in the hands of top judges on the country's Supreme Electoral Board.
But a controversial law pushed through by the AK Party last month has seen the judiciary come under greater government control, raising alarm in among other places, the European Union, which Turkey has been seeking to join for decades.
Last week 18 European MPs sent a letter to EU High Representative for Foreign Affairs Catherine Ashton urging her to request an invitation from Turkey for election observers.
"(There's) an atmosphere of mistrust, conspiracy, deep polarisation and sometimes aggression," Dutch liberal MP Marietje Schaake, who authored the letter, told Reuters.
"Instead of these elections representing a moment of calm, they could just add fuel to the fire."
With less than two weeks until polling day, it would be impossible to deploy a full observer team, Schaake said, but argued credible monitoring was vital to avoid controversy over the results sparking any further tensions.
"The stakes are high. For some individuals involved this is a fight for survival. I think it's in the interests of everyone that there are independent observers. It's better to be safe than sorry," Schaake said.
The EU does not normally monitor local polls, and Ankara has received no request for an invitation, a Turkish official told Reuters, although Erdogan has said international teams are welcome to monitor the vote if they wish to.
Erdogan was on the campaign trail on Thursday having on Wednesday angrily threatened to "ban a ban" imposed on his party's main campaign video after electoral authorities blocked it for misusing national symbols.
The video shows a shadowy figure cutting the cords on a huge Turkish flag, before loyal citizens rush to form a human flagpole to keep it flying. [ID:nL6N0MH2GD} (Additional reporting by Tulay Karadeniz; Editing by Jeremy Gaunt)