By Saif Hameed and Stephanie Nebehay
BAGHDAD/GENEVA (Reuters) - The final battle to recapture Falluja, Islamic State's stronghold near Baghdad, will start in ''days, not weeks'', a Shi'ite leader said Friday, as new reports of starvation-related death emerged from the besieged Sunni city.
The first phase of the offensive that started on Monday is nearly finished, with the complete encirclement of the city that lies 50 km (32 miles) west of the capital, said Hadi al-Amiri, the leader of the Iranian-backed Badr Organization.
Amiri, in military fatigues, spoke to state-TV from the operations area with Prime Minister Haider al-Abadi standing by his side, wearing the black uniform of Iraq's counter-terrorism force.
At the end of last year, Abadi said 2016 would be the year of the final victory over Islamic State, which declared a caliphate over adjacent Iraqi and Syrian territories two years ago.
Falluja is a bastion of the insurgency that fought the U.S. occupation of Iraq and the Shi'ite-led authorities that replaced Sunni leader Saddam Hussein.
It was the first city captured by Islamic State in Iraq, in January 2014, and the second-largest that remains held by the militants, after Mosul, their de-facto capital.
Amiri said this week the Shi'ite paramilitary coalition known as Popular Mobilization will only take part in the encirclement operations, and would let the army storm Falluja.
Popular Mobilization would only go in the city if the army's attack fails, he said.
The army has defused more than 250 explosive devices planted by the militants in roads and villages to delay the troops advance toward Falluja, state TV said, citing military officers.
The United Nations on Friday said about 50,000 civilians are prevented by the hardline Sunni militants from escaping Falluja.
Falluja's population was six times bigger before the war. Amiri called on the civilians to leave from a southwestern exit called the al-Salam (Peace) Junction.
People who managed to flee the city reported starvation-related death, the U.N. refugee agency UNHCR said. The Norwegian Refugee Council on Thursday reported similar accounts from displaced people interviewed at a camp near Falluja.
Only about 800 people only have managed to flee so far, mostly from the outlying areas of Falluja, UNHCR spokeswoman Melissa Fleming, told a news briefing in Geneva on Friday.
"Food has been in very short supply we are hearing accounts that people are relying on expired rice and dried dates and that’s about it for their diet.
"They have to rely on unsafe water sources, including drainage water from the irrigation canals," she added.
Health facilities and medications were not available.
The death toll since the start of the military operation on Monday reached about 50, including 30 civilians and 20 militants, a source in the city's main hospital said Friday.
Between 500 and 700 IS militants are in Falluja, according to a U.S. military estimate.
(Writing by Maher Chmaytelli, editing by Ralph Boulton and Angus MacSwan)