RIYADH (Reuters) - The speaker of Yemen's upper house of parliament died in Saudi Arabia on Monday from injuries suffered in a June assassination attempt on President Ali Abdullah Saleh, a government official with Saleh in Riyadh said. Abdulaziz Abdulghani is the first senior political figure to have died from the explosion in Saleh's palace mosque which forced the president and a number of his aides to seek medical treatment in Saudi Arabia. A former prime minister and vice president of North Yemen, Abdulghani will be buried in Yemeni capital Sanaa on Wednesday. Separately, the country's head of national security said 80 percent of the investigation into the source of the blast had been completed and the findings would soon be published. "The investigations... are on the verge of completion and all the plotters, instigators and perpetrators of this terrorist act will be revealed," said Ali Mohammed al-Ansi in remarks published in al-Methaq newspaper. Last week, a member of Yemen's ruling party said tribal leader and business tycoon Hamid al-Ahmar was the "prime suspect" in the attack on Saleh.