* Erdogan dismisses international concern
* President Gul has ruled out social media ban
* Rival parties warn of fraud in high-stakes vote (Adds Erdogan comments on social media)
By Jonny Hogg and Gulsen Solaker
ANKARA, March 20 (Reuters) - Turkish Prime Minister Tayyip Erdogan threatened to shut down Twitter and other social media platforms on Thursday and said he did not care about the international response, his latest outburst in an increasingly bitter election campaign.
Anger, threats and conspiracy theories have marked the run-up to the March 30 local elections, with Erdogan battling a corruption scandal he says is orchestrated by his enemies, much of it waged via leaks on Twitter and YouTube.
"Twitter, mwitter!," Erdogan told thousands of supporters at a rally in the northwestern province of Bursa, in a phrase translating roughly as "Twitter, schmitter!".
"We will wipe out all of these," he said.
"The international community can say this, can say that. I don't care at all. Everyone will see how powerful the Republic of Turkey is," he said in a characteristically unyielding tone.
Erdogan said two weeks ago that Turkey could ban Facebook and YouTube, which he says have been abused by his enemies after a stream of audio recordings purportedly revealing corruption in his inner circle emerged online.
President Abdullah Gul, a co-founder of Erdogan's ruling AK Party who is seen as a more conciliatory figure, later ruled out any such move.
The corruption scandal has further polarized Turkish society and raised the stakes in local elections now widely seen as a referendum on Erdogan's rule. Both sides have warned about ballot abuse, with the main opposition saying it alone plans to deploy half a million poll observers.
The AK Party is expected to follow suit.
Erdogan was shaken last June by anti-government protests, which have been rekindled in recent weeks partly by the graft scandal. But polls suggest his party is on course to maintain its dominance of the electoral map in the municipal vote, albeit with tight races in the major cities of Istanbul and Ankara.
"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 have people monitoring 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.
"ATMOSPHERE OF MISTRUST"
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.
The AK Party mayoral candidate in Ankara this week warned about the risk of "vanishing ink". Erdogan himself has told his supporters not to be duped by opponents using social media to try to trick them into inadvertently spoiling their ballots.
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.
With less than two weeks until polling day, it would be impossible to deploy a full observer team, Schaake said. But she argued that credible monitoring was vital to avoid controversy over the results sparking any further tensions.
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. (Additional reporting by Tulay Karadeniz and Humeyra Pamuk; Writing by Nick Tattersall; Editing by Jeremy Gaunt and Hugh Lawson)