* Abdullah camp broadcast audio on alleged vote fraud
* IEC Secretariat head Amarkhil denies authenticity
* Hundreds of Abdullah supporters protest in Kabul, Herat (Adds details from Abdullah news conference on phone intercepts)
By Mirwais Harooni and Hamid Shalizi
KABUL, June 22 (Reuters) - The party of Afghan presidential candidate Abdullah Abdullah broadcast audio on Sunday that it said showed mass fraud had been committed in an election that aims to transfer power democratically in the country for the first time.
The audio purports to show that Independent Election Commission (IEC) Secretariat head Zia-ul-Haq Amarkhil made phone calls to officials in several provinces ordering them to stuff ballot boxes using code words.
While Amarkhil denies the allegations and the Independent Election Complaints Commission is investigating, the broadcast could stoke further protests across the country supporting Abdullah's decision to withdraw from the vote.
The election comes at a delicate time as most foreign troops will exit by the end of the year, leaving behind a still strong Taliban insurgency and deepening economic crisis.
Abdullah, former leader of the anti-Taliban Northern Alliance, last week recalled his observers monitoring the ongoing count and said the outcome of the run-off with former finance minister Ashraf Ghani on June 14 would be illegal.
The United Nations has warned of an escalation of ethnic tension and called on him to reengage with the election.
Abdullah is of mixed heritage but his support base is with the Tajik community, while ex-World Bank economist Ghani is an ethnic Pashtun.
Ignoring U.N. and government calls to return to the process, Abdullah's party on Sunday used a news conference to air what it said were the intercepted phone call recordings of Amarkhil.
"Today we are releasing documents which show Amarkhil has organised cheating and manipulated votes favouring one candidate. In the coming days we will release more documents to the public," Baryalai Arsalai, Abdullah's campaign manager, said.
In one example, the voice instructs the person on the other end of the line to "stuff the sheep properly". The word "sheep" is interpreted by Abdullah's staff as code for "ballot box".
POWER STRUGGLE?
The authenticity of the audio was denied by Amarkhil, who told the Wall Street Journal on Sunday that he did not recall the conversations and "would never talk like that". Reuters was not able to reach him for comment.
The audio also includes alleged conversations in which the voice supposedly belonging to Amarkhil asks his staff to hire election workers based on their ethnicity, asking for more Uzbeks and Pashtuns, who mostly support Ghani.
The IEC deferred comment to the Independent Election Complaints Commission, which said it was looking into the allegations.
Tahir Zahir, a spokesman for Ghani, said: "It is very easy to duplicate someone's voice but a body with authority and the election complaints commission should investigate its authenticity."
There has been no official comment from the outgoing president, Hamid Karzai, who has not publicly supported either candidate. He was unable to stand for election again.
The broadcasts coupled with an apparent escalation in protests, so far only numbering in the hundreds or low thousands, have intensified longstanding concerns of a struggle for power along ethnic lines.
Several hundred of Abdullah's supporters protested outside the presidential palace, while others gathered and disrupted traffic for a second day on the main road leading to the international airport.
In western Herat province, hundreds of Abdullah supporters gathered and chanted "death to IEC" and "Fraudsters must be tried".
Protesters made their way to Herat governor's office and around 60 burnt their voting cards in protest.
"We are tired of fraud and we are against it," Abdul Rahman, a protester who burnt his voting ID in Herat, told Reuters.
"We had the right to cast one vote and when the Independent Election Commission does not respect our right then there is no need to have a voting card. We will not participate in elections any more."
In northern Kunduz province, armed men from Abdullah's campaign forcibly shut down the election office, Amir Amza Ahmadzai, head of IEC in Kunduz, told Reuters.
"We have already sent an official letter to the police but they haven't responded yet," he said. (Writing by Praveen Menon; Editing by Alison Williams)
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