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Tens of thousands of people are fleeing North Waziristan tribal region in north-west Pakistan after the army began an offensive against militants.

A camp for displaced people has been set up near Bannu but it lacks food, water and electricity, locals say.

Many displaced families are seeking shelter with friends and relatives.

A curfew has been lifted to allow people in North Waziristan to escape - and officials expect thousands more to flee to safety in the coming days.

"We have been locked inside our homes for the past four days ever since the curfew was imposed," Muhammad Niaz, from the town of Mir Ali in North Waziristan, told the BBC.

"The markets were closed and we ran out of food. I couldn't even take my child to the hospital. It was as if we were cut off from the world."

Media playback is unsupported on your device Media caption Families say they need more help from the government

Another man who had left his home, Khurshid Khan said: "I have come here with women and children. There was not a drop of water along the way. My son's face has gone yellow with thirst. And we still don't know where we are heading."

The army says at least 160 militants had been killed since it began air strikes on militant targets in Shawal and other areas of North Waziristan on Sunday.

There is no independent media access to the area and no way of confirming the casualty figures.

Tanks and troops are also being sent in for a full-scale operation to target Taliban and foreign militant networks based near the Afghan border, the military says.

Eyewitness: Riffatullah Orakzai, BBC Urdu, Bannu region

Displaced people are arriving carrying their few belongings and their children and trying to reach safety on foot, in the scorching heat.

They look tired and hungry. There are no places for them to stop and rest.

A few religious parties have now set up some relief camps along the way, with food and water, but not a single government camp could be seen.

Most of the families are choosing to stay with relatives and friends, because it is also considered culturally unacceptable to live as a displaced person in a camp.

On Monday, locals asked the government to allow them safe passage to leave the tribal agency.

The army had initially blocked all roads leading out of North Waziristan, ahead of the military operations.

Despite the lifting of the curfew, the government appears ill-prepared to accommodate the thousands who have been streaming out of the area since Wednesday.

Only one camp for internally displaced persons (IDPs) has been set up in the semi-autonomous tribal area of Bakakhel near Bannu.

Only three or four families have settled there. They say they have not been provided adequate food or water supplies in scorching summer temperatures. The area also has a proliferation of snakes and scorpions, another discouraging factor for families trying to seek shelter there.

North Waziristan is thought to have a population of between 550,000 and 700,000. Officials say approximately 80% of the population is still living in the area as the military strikes escalate.

In its latest statement on the fighting, the government said 15 militants had been killed by helicopter gunships in mountain heights to the east of the main town in North Waziristan, Miranshah.

It also said eight Uzbeks had been killed by army snipers while planting improvised explosive devices on the road between Miranshah and the town of Mir Ali.

Prime Minister Nawaz Sharif gave the go-ahead for the offensive after a deadly attack earlier this month on Karachi airport, which was claimed by an Uzbek militant group and the Pakistani Taliban.

Analysis: Saba Eitizaz, BBC Urdu

This new mass migration will be a major burden on the country's resources. Pakistan is already struggling to cope with almost two million people displaced during the military operations against militants in Swat in 2009.

Many of them have still not been able to return to their homes and are living in makeshift camps or in slums in Karachi.

The government is also still in the process of resettling IDPs from the devastating floods of 2010 that swept across one-fifth of the country and affected 20 million people.