TEHRAN:  The first plane carrying bodies of Iranian pilgrims killed in the hajj stampede in Saudi Arabia arrived in Tehran Saturday, nine days after the disaster that escalated tensions between the two regional rivals. President Hassan Rouhani and other senior officials were at the airport for the arrival of the plane, which carried 104 bodies. State TV says another flight is due later in the day. Saudi authorities say 769 pilgrims died in the stampede near Mecca in the worst disaster to strike the annual pilgrimage in a quarter-century. Iran appears to have lost the largest number of pilgrims, with 464 dead. Iran has blamed Saudi 'mismanagement' for the stampede, which took place after two waves of pilgrims converged on a narrow street, causing hundreds to suffocate or be trampled. It has also accused Riyadh of a cover-up, saying the real death toll exceeds 4,700, without providing evidence to support its claim. An Associated Press count based on figures provided from 15 of the 180 countries who sent pilgrims on the hajj this year indicates that at least 1,036 pilgrims died in the disaster. 'It should become clear whether some individuals were guilty in this incident or not. If it is proven that some officers were culpable, under no circumstances will we let the blood of our loved ones go in vain,' Rouhani said. 'In this incident, the language we have used has been the language of emotions, brotherhood and politeness and when necessary, we have used the language of diplomacy. If deemed necessary, the Islamic Republic of Iran will use its language of might,' he added, without elaborating. Iran has threatened to take international legal action against Saudi Arabia over the disaster, but it's unclear what avenues are available to it. The fallout from the hajj stampede has fed into the bitter regional rivalry between Sunni Saudi Arabia and Shiite Iran, which back opposite sides in the wars in Syria and Yemen. Saudi Arabia has launched an investigation into the stampede and says officials will be held accountable if it finds that mistakes were made. The hajj pilgrimage is one of the five pillars of Islam, and all able-bodied Muslims are required to undertake it once in their lives. This year some 2 million pilgrims took part in the hajj but Saudi Arabia has hosted more than 3 million in recent years without any major incidents.