The outlawed Kurdistan Workers' Party (PKK), which for years waged a deadly insurgency against Turkish authorities, called on all Kurdish armed groups Tuesday to unite against radical Islamist militants who have seized swathes of northern Iraq.

"Our efforts alone are not enough. There must be a joint (effort)" against the Islamic State (IS), the PKK's military leader Murat Karayilan said in remarks carried by the Radikal online newspaper.

His comments came after IS raised its black flag in the northern Iraqi city of Sinjar on Sunday after ousting the peshmerga troops of the Iraqi Kurdistan government, forcing thousands of people from their homes.

"Let's form a joint command. Let's make preparations and take IS out of the areas it occupied, including Sinjar. This is possible," Karayilan said.

Karayilan heads the military wing of the PKK, which has been involved in a now frozen peace process with Turkish authorities, in the absence of the PKK's leader Abdullah Ocalan who is jailed in a Turkish island prison.

The capture of Sinjar and several other towns at the weekend threatened to further integrate the Iraqi and Syrian halves of the "caliphate" IS leader Abu Bakr al-Baghdadi proclaimed in June.

Karayilan urged Kurdish groups to join ranks and form a "national resistance front" to fight against the jihadists to liberate Sinjar.

He also said peshmerga forces in northern Iraq could play a role. "They are better equipped. We can create a significant force."

On Monday, Baghdad's air force and Kurdish fighters from Syria joined forces with Iraq's embattled peshmerga to push back the jihadists.

Karayilan singled out main Kurdish parties in Iraq -- the Kurdistan Democratic Party and Patriotic Union of Kurdistan -- as well as the Kurdish People's Protection Units in Syria as needing to unite against the Islamists.

"We are ready to make every sacrifice... (we) could do this all together. We can support and join it. Our specialised forces could take part," he said.

In a statement on its website, the PKK said Monday none of the Kurds would remain silent to the "humiliating" attacks in Sinjar.

"Today is the day for unity and reinforced resistance!"

- Iraqi Kurds seek Turkish support -

Meanwhile, Turkish Foreign Minister Ahmet Davutoglu spoke on the phone with the president of Iraq's Kurdistan region Massud Barzani to discuss "the current situation in Iraq."

"We continue our consultations with all parties for stability in Iraq," Davutoglu wrote on his Twitter account.

A Turkish official told AFP that Barzani sought Turkey's support in the fight against the Islamist militants, who have been holding dozens of Turkish citizens including its chief consul in the northern Iraqi city of Mosul since June 11.

Barzani said Iraqi Kurds expected Turkey to help Kurds in the conflict with the IS and called for more consultations with Ankara, the official told AFP on condition of anonymity.

In return, Turkey vowed to support Iraqi Kurds with whom it has forged strong trade links in recent years, according to the official.

Turkey blacklisted IS -- known at the time as the Islamic State of Iraq and the Levant (ISIL) -- as a terrorist organisation in 2013.

The jihadist offensive in Iraq: a timeline
Baghdad (AFP) Aug 04, 2014 - Below are the main developments in Iraq, since Sunni Arab militants led by ultra-radical jihadists launched an offensive, seizing large swathes of territory in the north and the west of the country:

--JUNE, 2014--

- 10: Sunni Arab militants, led by jihadists of the Islamic State of Iraq and the Levant (ISIL), seize Iraq's second biggest city Mosul.

- 11: The insurgents seize executed dictator Saddam Hussein's hometown Tikrit, capital of Salaheddin province.

- 12: Kurdish forces take over Kirkuk to protect the northern oil hub from the militants, who have taken over several mainly Sunni Arab towns in the west of the province.

- 15: Militants take control of the Al-Adhim area in Diyala province, north of Baghdad.

- 19: The insurgents attempt to seize Iraq's biggest oil refinery outside the northern town of Baiji but after 24 hours of heavy fighting the army regains control.

- US President Barack Obama says Washington is prepared to send military advisers to study how to train and equip Iraqi forces.

- 20: Grand Ayatollah Ali al-Sistani, the highest religious authority for the Shiite majority, says the jihadists must be expelled quickly from Iraq and that the next government must avoid "past mistakes", an apparent rebuke to Nuri al-Maliki, premier since 2006 and accused of sectarian policies towards the Sunni Arab minority.

- 23: Insurgents overrun the strategic Shiite-majority northern town of Tal Afar and its airport.

- 29: ISIL declares an "Islamic caliphate" -- extending from Aleppo in northern Syria to Diyala province northeast of Baghdad. Renaming itself the Islamic State (IS), it declares its chief Abu Bakr al-Baghdadi "caliph" and "leader for Muslims everywhere".

--JULY--

- 3: Massud Barzani, the president of the autonomous Kurdish region asks its parliament to start organising a referendum on independence.

- 5: Baghdadi, appearing for the first time in a video released on social media, orders all Muslims to obey him.

- 9: Maliki accuses the autonomous Kurdish region of harbouring jihadists. The Kurdish authorities say Maliki has "become hysterical" and should step down.

- 15: In a rare sign of success, tribesmen and security forces succeed in driving out militants from Dhuluiyah, 80 kilometres (50 miles) north of Baghdad after days of heavy clashes.

- 18: Christians flee Mosul after mosques relay an ultimatum giving the minority a few hours to leave.

--AUGUST--

- 2-3: The IS conquers several Kurdish-held towns, including Sinjar and Zumar near the Syrian border, ousting Kurdish peshmerga fighters.

- 4: Maliki orders the airforce to provide support to peshmerga forces in their battle against jihadists.