German Foreign Minister Heiko Maas on Tuesday criticised plans to re-run Istanbul's mayoral election as "not transparent and incomprehensible to us".

"Who holds the office of Istanbul's mayor can only be decided by the will of the Turkish voters," Maas said in a statement.

"Maintaining democratic principles with transparent electoral conditions is our top priority."

With an estimated 2.9 million people of either Turkish citizenship or recent ancestry, Germany is home to the largest Turkish diaspora community worldwide.

Turkey's top election body on Monday ordered a rerun of March's Istanbul election after President Recep Tayyip Erdogan's ruling Justice and Development Party (AKP) complained of "irregularities" and "organised crime".

The main opposition Republican People's Party (CHP) has condemned the decision by Turkey's top election body to renew the election as "neither democratic nor legitimate".

Erdogan calls re-run the 'best step'

However on Tuesday, Erdogan welcomed the controversial order to hold a fresh Istanbul election after complaints of corruption as the "best step" for the country.

"We see this decision as the best step that will strengthen our will to solve problems within the framework of democracy and law," Erdogan told a meeting of his party members in parliament.

Erdogan on Tuesday talked of "organised crime" and "serious corruption" during the vote.

"The documents we have presented are quite solid and based on concrete evidence which cannot be disputed," he said.

"We sincerely believe there was organised corruption and irregularities."

He said that if his government did not bring to account the "thieves" who stole the "national will" at the ballot box, "our people will demand an explanation from us".

With 16 million residents, Istanbul is Turkey's economic engine and controls a major chunk of public spending.