* Erdogan's office says recordings "completely untrue"
* Leaked audio purportedly of Erdogan and his son
* Opposition calls for government to resign
By Nick Tattersall and Orhan Coskun
ANKARA, Feb 25 (Reuters) - Turkish Prime Minister Tayyip Erdogan's office described as a dirty immoral fabrication voice recordings purporting to reveal Erdogan telling his son to dispose of large sums of money on the day police raided houses in a graft inquiry into his government.
The recording posted on YouTube, whose authenticity Reuters could not verify, marked a sharp escalation in a graft crisis Erdogan's government says has been concocted by a U.S.-based cleric seeking to undermine his 11-year rule by using influence in the police and judiciary.
The growing political uncertainty hit Turkish markets amid broader weakness in emerging markets.
They appear a day after Erdogan aides said thousands of people, including senior politicians, had had their telephones illegally tapped over three years with the aim to blackmail and fabricate criminal cases.
The recordings are purportedly of Erdogan and his son Bilal discussing how to reduce the funds to "zero" by distributing them among several businessmen. At one point, the voice supposedly of Bilal says some 30 million euros ($40 million) remain to be disposed of.
Erdogan was elected to power in 2002 and remains far and away Turkey's most popular politician. But the apparent power struggle with cleric Fethullah Gulen, who has built up what the prime minister calls a "parallel state" has cast a shadow over what Western powers long vaunted as a prime example of an effective Islamic democracy.
Gulen, who controls a vast network of schools, businesses and media groups in Turkey and across the world, denies any involvement in the scandal and denies acting in an undemocratic manner.
The recordings appeared two days after Erdogan's AK Party officially began campaigning for local elections at the end of March that will be a key test of his enduring popularity.
"The recordings, which were released via the Internet this evening, accompanied with the allegation that they were a telephone conversation between our Prime Minister Recep Tayyip Erdogan and his son, are completely untrue and the product of an immoral montage," Erdogan's office said in a statement.
"Those who created this dirty conspiracy targeting the prime minister of the Republic of Turkey will be brought to account within the law," it said.
Erdogan held an emergency meeting with Deputy Prime Minister Besir Atalay, Interior Minister Ekfan Ala and intelligence chief Hakan Fidan after the recordings appeared, senior Turkish officials said.
He was scheduled to address a regular meeting of his party in parliament on Tuesday morning.
The leadership of the main opposition Republican People's Party (CHP) also met and party spokesman Haluk Koc called on the government to resign.
"Turkey cannot continue on its path with this dirt, this burden," Koc told reporters.
Erdogan's supporters say the graft investigation, which blew up on Dec. 17 with the detention of businessmen close to Erdogan and three ministers' sons, was contrived by U.S.-based cleric Fethullah Gulen. He has denied involvement.
The government has responded by dismissing or reassigning thousands of police officers, tightening its control over the appointment of judges and prosecutors, and pushing through a new law that allows the authorities to block access to websites within hours without a prior court order.
The growing political uncertainty hit financial markets.
The lira weakened sharply against the dollar after the new voice recordings emerged and traded at 2.2150 at 0850 GMT, slipping from 2.1750 on Monday. Shares dropped three percent.
Timothy Ash, head of emerging markets research at Standard Bank, said Erdogan was likely to go further on the offensive against those he deems responsible for producing and leaking these tapes.
"This seems to be a battle to the end/death. The Gulenists seem to want to wound Erdogan below the waterline to undermine the AK party's poll performance in March," Ash wrote in a note.
Social media and video-sharing sites have been awash with leaked recordings presented as evidence of wrongdoing. As with the latest recordings, Reuters has been unable to verify their authenticity.