more than 1,000 people, mainly civilians, have been killed and roughly the same number injured in fighting and other violence in Iraq this month as Sunni militants swept through the north, the United Nations has confirmed.

Victims include a number of summary executions committed by forces of the Islamic State of Iraq and the Levant (Isis) and prisoners killed by retreating Iraqi forces.

At least 757 civilians were killed and 599 injured in the northern provinces of Nineveh, Diyala and Saladdin from June 5-22, said UN human rights spokesman Rupert Colville.

"This figure - which should be viewed very much as a minimum - includes a number of verified summary executions and extra-judicial killings of civilians, police, and soldiers who were hors combat," he said. Others died in shelling and cross-fire.

At least another 318 people were killed and 590 injured in the same period in Baghdad and areas to the south, many due to at least six vehicle-borne bombs, said Mr Colville.

American Secretary of State John Kerry held crisis talks yesterday with leaders of Iraq's autonomous Kurdish region, urging them to stand with Baghdad in the face of the Sunni insurgent onslaught that threatens to dismember the country.

Iraqi security forces fought Sunni armed factions for control of the country's biggest oil refinery 120 miles north of Baghdad. It had been under threat for nearly two weeks since militants overran northern cities.

Abductions continue to be reported in the northern provinces and in Baghdad. They include 48 Turkish citizens abducted from Turkey's consulate when Isis captured Mosul and 40 Indian nationals working for an Iraqi construction firm who were also kidnapped.

Isis has broadcast dozens of videos showing cruel treatment, beheadings and shootings of hors de combat soldiers, police officers, and people apparently targeted because of their religion or ethnicity.

Navi Pillay, the UN High Commissioner For Human Rights, said last week that forces allied with the Isis had almost certainly committed war crimes by executing hundreds of non-combatant men.

Mr Colville said: "The evidence will be gathered just as it has been gathered for several years now in Syria against whoever is committing crimes, and hopefully one day there will be some accountability, but with groups like Isis/ISIL obviously it is particularly difficult."

Three civilians of the Shabak minority were captured by Isis in the Jazeer district of Mosul on June 18 and the bodies of two of them were found the next day, he said.

Fifteen Shi'ite civilians were abducted during an attack by Isis in Pirwajli village in Saladdin province and their bodies were later said to have been found by Iraqi troops.

The bodies of another 45 unidentified people were allegedly found on the banks of the Tigris River.

Iraqi government forces have also been reported to execute prisoners summarily, including not fully confirmed allegations involving the killing of 31 detainees at al-Qalaa police station in Tal Afar on June 15.

Mr Colville said the UN had confirmed the summary execution of prisoners by Iraqi forces as they withdrew from the Nineveh Operations Command in Mosul.

"In this case, grenades were reportedly thrown into rooms filled with detainees, killing at least 10 and injuring another 14," he said.