DUBAI, Sept 3 (Reuters) - Grand Ayatollah Sayyid Muhammad al-Hakeem, one of Iraq"s most senior Shi"ite clerics, died on Friday from a heart attack in the holy city of Najaf, Iraqi state news agency INA reported. Al-Hakeem, born in 1934, is one of four Grand Ayatollahs who teach at the Hawza, the religious seminary of Najaf, alongside Iraq"s top Shi"ite cleric, Grand Ayatollah Ali al-Sistani.