Islamic State fighters sweeping across Syria and Iraq are a direct threat to Britain and the country must use all of its "military prowess" to halt their advance, Prime Minister David Cameron said Sunday.

But the Conservative Party leader said he did not think British troops should be deployed in Iraq, and that he would consider working with Iran to combat the jihadist threat.

Writing in the Sunday Telegraph, Cameron warned that the West faces a "generational struggle".

"If we do not act to stem the onslaught of this exceptionally dangerous terrorist movement, it will only grow stronger until it can target us on the streets of Britain," he said.

"I agree that we should avoid sending armies to fight or occupy, but we need to recognise that the brighter future we long for requires a long-term plan."

Cameron argued that security could only be achieved "if we use all our resources -- aid, diplomacy, our military prowess."

He also said Britain needed to work with countries like Saudi Arabia and Qatar, Egypt, Turkey "and perhaps even with Iran".

A high-ranking Anglican bishop on Sunday slammed Cameron's Middle East policy in a letter that had the backing of Archbishop of Canterbury Justin Welby.

"We do not seem to have a coherent or comprehensive approach to Islamic extremism as it is developing across the globe," the bishop of Leeds, Nicholas Baines, wrote in the letter, sent to the Observer newspaper.

Defence Minister Michael Fallon said on Saturday that Britain would keep up its surveillance flights over northern Iraq to try to stop more minority groups coming under jihadist attack.

Britain deployed Tornado fighter jets to Akrotiri earlier this month, which will now be joined by the Royal Air Force's most modern surveillance aircraft, the Boeing RC-135 Rivet Joint.

Kurdish forces backed by US warplanes battled on Saturday to retake Iraq's largest dam from jihadist fighters, a day after militants carried out a "massacre" of dozens of villagers.

Two months of violence have brought Iraq to the brink of breakup, and world powers relieved by the exit of long-time premier Nuri al-Maliki were sending aid to the displaced and arms to the Kurds.

Kurdish forces attacked the Islamic State (IS) fighters who wrested the Mosul dam from them a week earlier, a general told AFP.

Iraq Yazidis fear for thousands kidnapped by jihadists
Bajid Kandala Camp, Iraq (AFP) Aug 16, 2014 - In a dusty, ill-equipped camp in northern Iraq, Yazidis fleeing a jihadist offensive say members of their families -- men, women and even babies -- have been abducted by militants.

The mass kidnappings by the Islamic State (IS) jihadist group targeted those who either refused or simply could not flee a string of villages around Mount Sinjar, one of the minority's main ancestral homes in northern Iraq.

The refugees say the women and children are being held in IS-controlled prisons in Nineveh province, where a sweeping jihadist-led offensive was launched in June, and that many of the men are feared to have been executed.

Khodaida Jarda, a man in his 60s wearing a light brown robe, plastic flip-flops and a dusty white turban, listed the names of his nine missing relatives.

His voice shook as he told AFP: "Please write down their names. My son, 26-year-old Haidar, is among the missing."

Other Yazidis, just as distraught, gave similar accounts.

"My two cousins and my two uncles were kidnapped," said Jacqueline Ali, a 17-year-old high school student now sheltered at the Bajid Kandala camp near the Tigris River, in the autonomous Kurdish region of northern Iraq.

Cradling her sister's infant, she spoke quietly as her large brown eyes welled up with tears.

"Their sisters and mothers are so scared for them that they have been refusing to eat since we arrived in the camp. We are really afraid for them," said Ali.

Amnesty International, which has been documenting the mass abductions, says thousands of Yazidis have been kidnapped by IS since an August 3 onslaught on their villages began.

The attack pushed the Yazidis out of their villages near the Iraq-Syria border. Survivors fled onto Mount Sinjar, where they were besieged by IS for days with little food or water.

- 3,000 women, girls abducted -

Some 200,000 people escaped to safety in Iraq's Kurdish region, but others remain on the mountain, and Amnesty International's Senior Crisis Response Adviser Donatella Rovera said the fate of "thousands" of abductees remains uncertain.

"The victims are of all ages, from babies to elderly men and women," she told AFP.

She also said the kidnappings all appear to have happened in villages where residents dared to take up arms against the jihadists.

While IS has a track record of kidnapping in Syria, the group has not previously rounded up women and children en masse.

"It seems they took away entire families, all those who did not manage to flee," Rovera said.

Among the abductees are some 3,000 women and girls, who are being held separately from the men in IS-controlled Tal Afar east of Mount Sinjar, she said.

"We fear the men may have been executed," Rovera added, describing the kidnappings as a "crime" under international law.

Two women -- Leila Khalaf and Wadhan Khalaf -- were among those kidnapped from Mujamma Jazira village, said their relative Dakhil Atto Solo, adding that the abductions happened after residents tried to resist the IS attack.

"Of course we tried to defend our villages, but they had much bigger weapons. All we had were our Kalashnikovs," said Solo.

"They executed 300 men, and took the women to their prisons. Only God can save them now," he said.

Their children, said Solo, were rescued by the family.

"But the women were in a house surrounded by IS. We had to escape. Now, the children cry for their mothers all the time. 'Mama, mama,' they wail. But there is no mama, we tell them."