NAJAF, Iraq (Reuters) - In early September, Ayatollah Mahmoud Hashemi Shahroudi, a senior Iranian official and cleric, flew to the holy city of Najaf in southern Iraq. His entourage included a sizable security detail and the former head of the Revolutionary Guards, the most powerful military force in the Islamic Republic. Shahroudi, 69, spent several days on a charm offensive meeting officials, clerics and seminary students at his office near the golden dome shrine of Imam Ali, one of the world s holiest Shi ite sites. His aim was to raise his profile as a replacement for the top Shi ite cleric and most powerful man in Iraq: the 87-year old Ayatollah Ali Sistani, according to current and former Iraqi officials. While attention has focused on Iraq s battle against Islamic State, the country s future could equally hinge on what is happening in Najaf. With Sistani s advanced age and persistent rumors about his health, the question of his replacement has become more pointed. Iraqi Shi ite factions are jockeying to influence who replaces Sistani. Iran, whose population is mostly Shi ite, backs Shahroudi. Shahroudi could prove a controversial replacement for Sistani. Senior clergy in Najaf are wary of Iran trying to expand its influence and Shahroudi is viewed with some suspicion, although he could still build support among students. Since Sistani has distanced himself from Iranian politics some of his followers may not want a replacement who is close to Tehran. Sources in Najaf were unwilling to go on the record on a matter as sensitive as Sistani s successor, but a former senior Iraqi official told Reuters:  The Iranians will try their best.   It s not just religious, politics have become part of it. It will decide the fate of Iraq,  the official said. Iran has already expanded its influence in Iraq by helping the Shi ite-led government in Baghdad retake disputed areas from the Kurds. The head of the branch of the Revolutionary Guards responsible for operations outside Iran, Qassem Soleimani, personally convinced some Kurdish leaders to abandon their claim to contested towns, like the oil-rich Kirkuk. Attempts to reach Shahroudi and the Revolutionary Guards media office were unsuccessful, as were attempts to reach Sistani s office for comment. If Iran can influence who becomes the next top Shi ite cleric in Iraq, it could tighten its grip on power within the country for years. A senior cleric in Najaf who is sympathetic to the interests of Iran would also eliminate a rival to Iranian Supreme Leader Ayatollah Ali Khamenei, who claims to be the leader of Shi ite Muslims worldwide. For years, Sistani, who has endorsed a religious and political viewpoint independent of Iran, has been Khamenei s top challenger for the leadership of the global Shi ite community. Sistani is rarely seen in public but his decrees are sacrosanct to his millions of Shi ite followers. Sistani s fatwa to rise up against the Sunni militants of Islamic State thwarted the group s push toward Baghdad in 2014. The cleric has also used his decrees to reduce sectarian violence in the country. Sistani opposed the secession of the Kurdish region after the referendum on independence in September but then urged Baghdad to protect Kurds after reports of abuses surfaced last month. Without Sistani s restraining influence, clashes are likely to break out between sects as well as among rival Shi ite groups, Iraqi officials and observers say.  Sistani is not just a poor guy sitting in a house. He can control millions of people,  the Iraqi former senior official said.  It will be a very bloody struggle after Sistani passes away.  Sources in Najaf expect Sistani to remain in his post until his death. There is no clear succession process, but Shahroudi would need to obtain the support of a large number of ordinary Shi ites, seminary students and other clerics. Shahroudi is no stranger to Najaf: he was born in the city to Iranian parents. In the 1970s he was jailed and tortured by Saddam Hussein s security forces because of his political activities. He moved to Iran after the Islamic revolution and has been promoted to top posts since Khamenei became supreme leader in 1989. Shahroudi was head of the Iranian judiciary for a decade and is currently the head of the Expediency Council, a body intended to resolve disputes between parliament and a hardline watchdog body, the Guardian Council. In public, Shahroudi is often seen sitting next to Khamenei. Shahroudi s visit is only one sign of how Tehran is trying to rally support for its candidate to replace Sistani. A company linked to the Revolutionary Guards is involved in a $300 million project to expand the Imam Ali shrine, making it the second largest Muslim holy site after Mecca in Saudi Arabia.  These projects create a state of dependency between recipients of aid and Tehran since they integrate the Iraqi infrastructure into the Iranian infrastructure network,  said Ali Alfoneh, an expert on the Guards at the Atlantic Council.  Furthermore, such activities provide a cover for the Islamic Republic s intelligence networks operating in Iraq.  In 2011, Shahroudi opened an office in Najaf and began paying clerical students stipends, which observers say was an attempt by Iran to increase its influence.  It was a provocative move,  said an Iraqi analyst familiar with the Shi ite clergy who asked not to be identified. Shahroudi subsequently opened offices in Baghdad and Karbala. He pays stipends to thousands of seminary students, according to Iraqi officials and clerical sources in Najaf.  Clerics often pay stipends to students to gather support, raise their profile and perhaps become accepted as a marja, or top cleric, observers say.  Iran is trying to influence the process of who comes after Sistani through the students,  said a Western diplomat in Iraq who did not have permission to speak on the record. Sistani is now the main sponsor of Shi ite clerical students, paying millions of dollars in Iraq and elsewhere. His son Mohammed Ridha oversees the financial and administrative work of his office.  Follow the dollars to see what will happen next,  said an Iraqi senior official familiar with the clerical politics of Najaf.  Mohammed Ridha Sistani controls all the cash.  Mohammed Ridha s work could position him to replace his father, observers say, though passing the religious mantle within a family would be unprecedented in Shi ite custom. Top contenders to replace Sistani in Najaf include three other marjas but they are old and there is no clear front-runner, according to clerical sources and Iraqi officials.  Nothing is fixed to make a decision for this procedure,  said Sheikh Ali Najafi, son of one of the top Najaf marjas.  While in Iraq, Shahroudi visited prime minister Haidar al Abadi in Baghdad. Iraqi officials said Sistani refused to see him in Najaf, but they do not expect the Iranians to give up. 