Robert Mueller's special counsel probe arrested a business associate of Mike Flynn, Donald Trump's disgraced national security adviser, Monday - on the eve of the retired general's sentencing and after the president criticized the case against him.

Bijan Kian, an Iranian-American who was number two to Flynn was arrested and appeared in federal court in Washington D.C. before being freed on bail.

He is charged with a plot to lobby without declaring that he and Flynn's firm was working for the Turkish government, breaking the Foreign Agent Registration Act which makes it illegal to lobby for foreign governments without registering with the State Department. Kian has yet to enter a plea.

Also indicted was the business partner who worked with him and Flynn, Turkish-Dutch dual national Ekim Alpetkin, who is the subject of an arrest warrant and thought to be in Turkey.

Kian and Alpetkin are accused in court papers of a plot to convince the U.S. government to extradite or otherwise expel Fethullah Gulen, a Turkish cleric who is a deadly rival of the country's strongman president Recep Tayyip Erdogan.

Mueller says in the court papers that with Flynn, who is referred to a 'Person A' they placed an op-ed in The Hill newspaper without acknowledging that it was at the prompting of the Turkish government.

Flynn wrote the op-ed and his firm, The Flynn Intel Group, was paid $600,000 for their lobbying campaign - but he is not indicted himself in what appears to be a sign that he flipped on his former associates.

The retired general, who is due to be sentenced on Tuesday for lying to the FBI related to his contacts with the then Russian ambassador to the United States, Sergei Kislyak, has also admitted to lying about his role in the Turkish lobbying effort and has been cooperating with prosecutors on the probe.

The special counsel has praised the former Trump administration official for his 'substantial help' in several investigations. It is believed this is one of them.

Bijan Kian (left) and Turkish businessman Ekim Alptekin (right) were indicted for their work with former Trump National Security Adviser Michael Flynn on a lobbying project for Turkey

The indictments are part of special counsel Robert Mueller's broader crackdown on foreign lobbying

Relations between President Trump and Turkish President Erdogan have been on a rollercoaster

Bijan Kian with Michael Flynn: The company the two ran - The Flynn Intel Group - was paid $600,000 by the Turkish government to influence public opinion without declaring who their paymasters were - which is illegal

The timing of the arrest and indictments appears extremely pointed.

Flynn is due in court Tuesday to be sentenced after the Mueller probe released documents offering insight into his prosecution which have fueled claims from Trump and his supporters that the former adviser was railroaded into a 'perjury trap'.

They showed that agents did not advise him to bring an attorney and did not explicitly tell him that lying to the FBI is a felony, leading to accusations from Trump and others that the process was an abuse of power, and that Flynn's sole offense was a technical one.

But Mueller hit back hard Friday with court papers saying that Flynn was a former senior military officer and government official who did not need warned lying to the FBI is a crime.

His latest move Monday addresses the other aspect of the criticism - that Flynn did no other wrong - by putting him at the heart of a plot to effect change on U.S. policy as it affects a key ally without admitting who was paying for the effort to change it.

The indictments are part of Mueller's look into foreign lobbying and outside attempts to influence U.S. policy abroad.

TURKISH CLERIC WHO IS AT CENTER OF CASE The indictment of Mike Flynn's business partner and their associate puts a controversial Turkish cleric in the spotlight. Mohammed Fethullah Gulen has been an exile in the Salyorsburg, PA, since 2001 but remains a hugely significant figure in Turkey. He is the leader of a movement called Gulen which sharply divides opinion. To its backers it is an attempt to allow people of Muslim faith to fully participate in the explicitly, and sometimes militantly, secular Turkish government. But to its opponents it is an attack on the Turkish establishment which risks destabilizing the country. Turkish cleric and opponent to the Erdogan regime Fethullah Gulen at his residence in Saylorsburg, Pennsylvania In the past Turkey's president, Recep Tayyip Erdoğan, was a significant backer, and the two were allies, both promoting a political Islam. But by 2013 their alliance had come unglued. When the military made a string of arrests among Erdogan's allies on allegations of corruption, Erdogan and other political parties responded that Gulen was behind them and trying to unseat the government. It was said that Gulen orchestrated the plot in retaliation for the Turkish government shutting down his movement's schools. Gulen protested his innocence from his U.S. home in exile but in 2016 he was accused of being the mastermind of a bigger threat to Erdogan - a botched coup. This time the Turks demanded his extradition in July 2016, but the Obama administration turned them down, setting of the lobbying effort through disgraced Mike Flynn. The truth of the competing claims about Gueln are almost impossible to settle accurately. He has spoken out against Islamic terrorism, in favor of secular democracy and Turkey joining the European Union. But secularists in Turkey see the movement as turning the country towards political Islam, and against the secularist ideals of its founder Kemal Ataturk. It has been accused of being a cult and compared to Opus Dei, the secretive conservative movement inside the Catholic Church. It the Netherlands, the Dutch government ordered an investigation by its security forces which found it was religiously conservative but did not encourage radicalization or violence, and that its members contributed successfully to society. Gulen's movement is unarguably rich, with one estimate putting its worth at a total of as much as $50 billion, spread across not just Turkey but the U.S., Europe and parts of Asia. The exiled cleric's appearance in the Flynn court case is unlikely to be his last in U.S. courts; the Trump administration has asked the Justice Department to investigate whether there could be grounds for his deportation, a move which would inevitably lead to a legal challenge - one which would force U.S. judges to consider what actually is the fiercely contested truth about the controversial cleric. Advertisement

Former Trump campaign manager Paul Manafort was indicted for his work for the Ukraine - and more significantly for those close to Trump, efforts to gain influence by Middle Eastern countries including Qatar, Saudi Arabia and the United Arab Emirates - of which the latter two have become close allies of Jared Kushner, the president's son-in-law.

The Turkish investigation ensnared Flynn and his two partners.

The indictment alleges that Rafiekian and Alptekin made false statements about the project in filings to the Department of Justice in order to mask the involvement of the Turkish government, which had been pushing for the extradition of Gulen, identified only as a Turkish citizen in the indictment.

'The defendants sought to discredit and delegitimize the Turkish citizen in the eyes of politicians and the public, and ultimately to secure the Turkish citizen's extradition,' attorneys for the Eastern District of Virginia wrote.

A representative for Alptekin, 41, said she did not immediately have a comment.

A lawyer for Rafiekian, a 66-year-old former director at the U.S. Export-Import Bank, declined to comment.

Turkish officials were not immediately available for comment.

Erdogan has blamed Gulen for stoking a failed coup against him in 2016. Gulen denies that.

Flynn's work on the Turkey project came under scrutiny after he published a commentary on The Hill on the day of the 2016 presidential election calling Gulen a 'radical Islamist' who should be extradited to Turkey.

The op-ed blamed Gulen for the July 15, 2016 coup that attempted oust the Turkish president and 'urged the U.S. government to deny the Turkish citizen refuge in the United States.'

Turkish President Recep Tayyip Erdogan has accused Gulen of directing the failed coup, which Gulen has denied.

Gulen denies being a radical Islamist. Both he and Erdogan were allies who came to power on a platform of political Islam before falling out.

Turkey has been trying to extradite Gulen since 2016 but the Justice Department has denied the request, saying it did not meet the 'legal standards' for extradition.

The indictment also shows how Flynn was texting and emailing frequently about the project throughout the final weeks of the presidential campaign, when he was advising Trump on foreign relations.

Along with the editorial, the Flynn Intel Group produced a report on Gulen and footage for a documentary that was never made. Of the roughly $600,000 paid to Flynn's company, $80,000 was sent back to Alptekin through his Netherlands-based firm Inovo BV, Justice Department filings show.

While Alptekin has previously claimed the $80,000 was sent back to him as repayment for work that was never finished, the indictment contends the money was part of a pre-arranged plan to kick back 20 percent of the project to Alptekin.

Alptekin, who was chairman of the Turkey-U.S. Business Council, has told Reuters previously that the payments to Flynn came from him personally and from Inovo, and were not from the Turkish government.

During an interview with the FBI, Alptekin said that while he had discussed the project with a Turkish government minister he decided to go ahead and retain the Flynn Intel Group himself after the Turkish government 'dropped the ball'.

Among other evidence, the indictment cites an email from Alptekin to Rafiekian and Flynn in August 2016 in which Alptekin says that he had spoken about the project to discredit Gulen with two Turkish ministers and had a 'green light to discuss confidentiality, budget and the scope of the contract.'

The indictment also cites a Sept. 19, 2016 meeting in New York which sources familiar with the matter say was between Rafiekian and Flynn and Turkey's foreign minister, Mevlut Cavusoglu, and energy minister, Erdogan's son-in-law Berat Albayrak.

The deal with Flynn was approved at top levels of the Turkish government, the indictment said, with Alptekin keeping senior ministers apprised of its progress.

The indictment came one day ahead of the planned sentencing of Flynn, who was arrested last year over his secret dealings with Russian officials and Turkey.

Flynn admitted one count of lying to the FBI in a plea deal which led to him providing "substantial" information to Special Counsel Robert Mueller's investigation into Russia meddling in the 2016 election.

Flynn's work with the Turks has been known since last year, when the Wall Street Journal reported that he, Rafiekian and Alptekin met Albayrak and Cavusoglu in New York in September 2016.

At that meeting they discussed physically removing Gulen from his Pennsylvania home to Turkey without a legal extradition order.

The Journal cited former CIA director James Woolsey, who attended the same meeting and later told reporters he found the idea possibly illegal.

That conversation was followed in the ensuing weeks by visits by Rafiekian and others to see, among others, a member of Congress and a congressional staffer in an attempt, among other things, to prompt congressional hearings on Gulen.

Attack: Trump has thrown himself behind criticism of the Robert Mueller special counsel probe and its dealings with Flynn after court papers showed how Flynn was not told lying to the FBI was a crime. Mueller's response has include arresting his business partner

Last month, President Trump said he was not considering Turkey's extradition request.

'No, it's not under consideration,' he said of Gulen. 'We are looking, always looking, and whatever we can do for Turkey and, frankly, countries that we can get along with very well. We're having a very good moment with Turkey.'

Trump said he gets along 'very, very well' with Erdogan and called him a 'friend of mine.'

'Whatever we can do, we'll do,' Trump added. 'But that is something that we're always looking at. But at this point, no.'

U.S.-Turkish relations have been on a bit of a roller coaster under Trump.

They were on an upswing in the wake of American cleric Andrew Brunson's release from a Turkish prison in October.

And Trump reportedly fist-bumped Erdogan when they met in Brussels this past summer at a NATO meeting and praised the Turkish president – who is known for his authoritarian style – a leader who 'does things the right way.'

But things went back downhill after Trump's refusal to lay the blame for the murder of journalist Jamal Khashoggi at the feet of Saudi Prince Mohammed bin Salman, whom Turkish intelligence blamed and U.S. intelligence agencies suggested he was involved.

Tensions between the two have also flared around Syria.

Trump called his Turkish counterpart on Friday and asked him to call off Turkey's military strike against the U.S.'s Kurdish partners in Syria.

It's unclear if the two leaders reached a deal but they agreed 'on the need for more effective coordination' in Syria, an official told The Wall Street Journal.

Prosecutors charge the two men 'conspired covertly and unlawfully to influence U.S. politicians and public opinion' regarding Fethullah Gulen (above), a cleric living in Pennsylvania that Turkish President Recep Tayyip Erdogan has accused of directing a failed coup

Prosecutors charge that Kian and Alptekin 'conspired covertly and unlawfully to influence U.S. politicians and public opinion' regarding Gulen to try and 'ultimately' secure Gulen's extradition.

The two men 'knowingly acted and caused others to act in the United States as an agent of a foreign government, that is, the government of Turkey, without prior notification to the Attorney General, as required by law,' the indictment reads.

The 21-page indictment lays out how the two men established their work against Gulen, what work was performed, how they covered up the fact the Turkish government was involved and their payment for the project.

The Flynn Intel Group received $600,000 for their efforts to discredit Gulen.

Kian, also known was Bijan Rafiekian, is referred to in the indictment of being a co-founder of the Flynn Intel Group, which 'offered various services' to it clients based on Flynn's 'national security expertise.'

Alptekin is identified as a 'dual Turkish-Dutch citizen residing in Istanbul' with 'close ties to the highest levels of the Government in Turkey.'

He owned a company based in the Netherlands that paid the Flynn Intel Group for its work.

The Flynn Intel Group wired $40,000 to Alptekin's company in the Netherlands in what it called a 'consultancy' fee, the indictment revealed. But it was actually payment to Alptekin's for pretending he was Flynn's client when the Flynn Intel Group knew that its client was really the Turkish government.

The 'Government of Turkey directed the work through Alptekin' but the 'defendants sought to conceal Turkey's involvement in the efforts to discredit,' the indictment notes.

Prosecutors also accuse the two men of 'knowingly provided false information' to the company's attorneys 'in an effort to hide' the 'involvement of Turkish government officials in the project.'

Ekim Alptekin remains in Turkey

Flynn is referred to in the indictment only as 'Person A.'

The Flynn Intel Group is now defunct.

When he pleaded guilty last December to lying to FBI gents working on the Russia investigation, Flynn also admitted to repeated violations of laws requiring firms to register their work on behalf of foreign clients.

Flynn is scheduled to be sentenced on Tuesday in that case, the first former White House official to face the judge.

Last week Mueller's office said that Flynn's cooperation - including 19 meetings with investigators - was so extensive that he was entitled to avoid prison when he is sentenced.