Iraqs top Shiite Muslim cleric said on Friday that a new prime minister must be chosen without foreign interference after the incumbent Adel Abdul Mahdi announced his resignation a week ago. Grand Ayatollah Ali al-Sistani urged political leaders to abandon partisan politics in choosing a new head of government and said he would have no involvement in efforts to replace Abdul Mahdi. Young protesters have thronged Baghdad and the Shiite-majority south since October, accusing the entrenched political elite of corruption and incompetence. Last week, they brought down Abdul Mahdi, who resigned after Sistani urged lawmakers to reconsider their support for the government following two months of anti-establishment protests where security forces have killed more than 400 demonstrators. "We hope a new head of government and its members will be chosen within the constitutional deadline" of 15 days since the resignation was formalized in parliament on Sunday, a representative of Sistani said in his Friday sermon in the holy city of Kerbala. "It must also take place without any foreign interference," he said. Iraqs main political blocs have been debating candidates for the premiership but have yet to name anyone. Two key foreign officials have attended the talks, according to a senior political source -- Irans pointman for Iraq Major General Qasem Soleimani and Mohammad Kawtharany, a leading power-broker from Lebanons Hezbollah movement. Iran, in particular, wields tremendous sway among Iraqi political and military figures, especially the Hashed al-Shaabi paramilitary force. But the protesters on the streets have publicly rejected what they say is Irans overreach and have vented their anger against its diplomatic missions. On Thursday, demonstrators were rattled by the sudden arrival of several thousand Hashed supporters in Baghdads Tahrir (Liberation) Square, the epicenter of the protests. In an apparent show of force, the newcomers waved sticks, national flags, and the Hasheds emblem -- a symbol shunned by the vast majority of protesters. The Hasheds political arm, the Fatah bloc, had been one of the prime ministers main backers throughout the crisis but changed its tune after Sistanis call. The Hashed began publicly supporting the protests and Sistani on their social media pages -- while repeatedly claiming there were "infiltrators" within the crowds. Demonstrators have expressed doubts about the genuineness of the Hasheds support, saying Thursdays display was an attempt to "ruin" their non-partisan rallies. Apprehensive about a repetition on Friday, protesters said they would erect new checkpoints around the square overnight. Tahrir has become a melting pot of Iraqi society, occupied day and night by thousands of demonstrators angry with the political system in place since the aftermath of the US-led invasion of 2003 and Irans role in propping it up. - Photographer abducted - Their public criticism of leading Iranian figures, including Soleimani, has broken a taboo and some among the protesters fear there will payback. Many in Tahrir keep their faces covered, saying they have been filmed or photographed by individuals that they suspect are "not real protesters." They worry they could be kidnapped or worse if they are identified as having opposed Iran or its allies, or simply for taking part in anti-government rallies. Earlier this week, the bruised body of 19-year-old Zahra Ali was left outside her family home, after she went missing from the morning, her father said. And on Friday, the relatives of Zeid al-Khafaji, a young photographer who had become well-known in the square, said he too had been kidnapped. They said he had been snatched from outside his home by unidentified men in SUVs as he was returning from Tahrir. Human rights groups have documented dozens of cases of abductions since October and Human Rights Watch this week accused the government of not doing enough to protect activists.