* Erdogan in power struggle with U.S.-based Turkish cleric
* Four new voice recordings aired on internet
* President orders review of Turkish ability to tackle graft
By Humeyra Pamuk
KIRIKKALE, Turkey, March 4 (Reuters) - Prime Minister Tayyip Erdogan on Tuesday berated an Islamic cleric he accuses of plotting to wreck his government, as more voice recordings apparently intended to embarrass the Turkish leader were aired on the Internet.
Erdogan is locked in a power struggle with U.S.-based Turkish cleric Fethullah Gulen, a former ally he says is behind a stream of "fabricated" voice recordings purportedly revealing corruption in the prime minister's inner circle.
Four more recordings have appeared on YouTube in the last two days, part of what Erdogan sees as a campaign to undermine his ruling centre-right AK Party before local elections on March 30 and a presidential poll due later this year.
Amid the allegations that have rattled financial markets and raised questions over Turkey's political stability, President Abdullah Gul on Tuesday ordered a state audit of the country's capacity to tackle corruption.
Rounding on the Gulen movement in an election campaign rally in the central Turkish city of Kirikkale, Erdogan, the country's most popular politician, was in characteristically defiant mood.
"We will make them (Gulen's movement) regret these coup undertakings... We will reveal their blackmail and threats one by one ... Those who have betrayed this country will pay the price," Erdogan told a crowd of about 5,000 supporters.
In one of the recordings leaked on Tuesday, Erdogan purportedly tells a well-known shipping magnate to appeal the result of a multi-billion-dollar tender to build six frigates after Koc Holding, Turkey's biggest company, won a contract to build four of the warships in January 2013.
The contract was eventually awarded to the naval shipyards. A second contract to build a helicopter landing dock went to a Turkish-Spanish joint venture. The national warship project had initially favoured wholly domestic, private-sector producers.
Erdogan has publicly signalled a dislike for Koc Holding, suggesting that the company, whose output accounts for about 10 percent of the economy, has meddled in politics. Koc and its subsidiaries have faced a series of fines, lawsuits and tax audits in recent years.
Koc could not be reached for comment on Tuesday. Erdogan's office has declined to comment on the latest recordings.
Another voice recording, posted late on Monday, purports to be of Erdogan urging his justice minister to speed up a court case against Aydin Dogan, head of a family-run conglomerate seen as part of a secular elite which has had an often tense relationship with his Islamist-rooted government.
Dogan said in a statement carried by its newspaper Hurriyet that the conversation, if true, would mark a "clear interference in the judicial process" that it said risked shaking trust in the rule of law in Turkey. Erdogan's office declined to comment.
Government officials say Gulen's Hizmet network has been illegally tapping thousands of telephones in Turkey for years to concoct criminal cases against its enemies and try to influence government affairs. Gulen has denied the accusations.
At Tuesday's rally in the AK Party's conservative heartland - the men and the mostly headscarved women stood separately - there was no sign of any wavering in support for Erdogan as he battles the biggest challenge to his 11-year rule.
"I believe there is corruption but look at how much Turkey has progressed under the AK Party. We used to have to pay a lot of money in interest, but Erdogan has been investing in the country," said Ali Osman Celik, 38, a shopkeeper.
Earlier in the day, President Gul said he had instructed the State Supervisory Council to examine regulations governing the wiretapping of communications as part of a review of Turkey's capacity to tackle graft in state institutions.
Gul also asked the auditors to look at the process by which judges and prosecutors are chosen and to assess rules surrounding "state secrets".
Last month, parliament approved a new law tightening control of the judiciary, a move Erdogan's critics say is a further attempt to snuff out the corruption allegations after the government dismissed or reassigned thousands of police officers and hundreds of judges and prosecutors.