BAGHDAD, Iraq (CNN) -- One of Iraq's top Shiite leaders died Wednesday, a senior official with his office told CNN.
Abdul Aziz al-Hakim died in Tehran, Iran, and his body will be sent to Iraq to be buried in Najaf, said Haitham al-Husseini, a senior official with al-Hakim's office who was one al-Hakim's advisers.
Al-Hakim had been receiving lung cancer treatment in neighboring Iran for more than two years.
He recently "experienced a setback in his health condition which required he be readmitted to hospital, where he is under the careful supervision of a specialized medical team," his party said in a statement.
His party asked people to pray for him Sunday.
Al-Hakim headed the Islamic Supreme Council of Iraq (ISCI), which once was arguably Iraq's most powerful Shiite political party. It lost much of its influence recently, notably in last January's elections, when politicians allied with Prime Minister Nuri al-Maliki won control of most of Iraq's provincial councils.
After his condition was made public in 2007, al-Hakim spent most of his time being treated in Iran. He had been grooming his son Ammar al-Hakim to take over.
Abdul Aziz Al-Hakim spent years in Iran as an exile, but returned to Iraq in 2003 following the overthrow of Saddam Hussein. He had been an ally of both the United States and Iran.