ISTANBUL (Reuters) - Turkish state lender Halkbank on Thursday denied allegations that it was involved in illegal transactions designed to help Iran avoid U.S. sanctions, following testimony in New York against its former deputy general manager.   Our bank has not been a part to any transaction which is uncertain and illegal relating to any country and has not executed any transfer transaction which is uncertain and unlawful,  it said in a statement.  There is no systematic and conscious violation of transactions... as it is alleged and it has not been intermediated in the export of prohibited parties and goods.  Its comments came after Iranian-Turkish gold trader Reza Zarrab on Wednesday told a U.S. federal court that he helped Iran use funds deposited in Halkbank to buy gold that was smuggled to Dubai and sold for cash.  Zarrab, who has pleaded guilty, is testifying against Halkbank executive Mehemt Hakan Atilla, who has pleaded not guilty.    