Iraq's leader, Nouri al-Maliki, has welcomed Syrian jets bombing near a border post lost by his forces to insurgents, in a rare strike against the jihadist group Isis that also occupies much of northern Syria.

Maliki acknowledged that a series of attacks on Tuesday targeting the Islamic State in Iraq and the Levant (Isis) near the town of al-Qaim, on the Iraqi-Syrian border, were carried out by the Syrian air force.

Joshua Earnest, White House spokesman, said earlier that the US had "no reason to dispute" reports that Syria had attacked within Iraqi territory but Maliki told the BBC that the air force had stuck to its side of the border. Maliki said the Syrian air strike on the Sunni militants left both countries "winners" but claimed his administration had no prior warning of the raids.

"There was no coordination involved, but we welcome this action. We welcome any Syrian strike against Isis because this group targets both Iraq and Syria ... But we didn't make any request from Syria. They carry out their strikes and we carry out ours. The final winners are our two countries," he said in an interview with BBC Arabic.

An initial translation supplied by the BBC said Maliki had confirmed Syrian air strikes in Iraq but this was later corrected to Syria.

The embattled Iraqi prime minister has asked for urgent help with air strikes to halt the advance by Isis, which has seized a 500-mile (800km) stretch of the border, two cities and almost one third of Iraq in a stunning sweep through northern and western areas in the past two weeks.

The US air support he urgently requested has been slow in coming though, with Washington reluctant to send its air force back into combat in Iraq in the absence of political unity among its leaders.

Maliki has also turned to Iran, which quickly sent a small force of troops to Iraq in the early days of the insurrection and has since sent arms and ammunition and senior officers to help defend Baghdad.

Tehran has played a similar role for the past three years in propping up the regime of Syria's leader, Bashar al-Assad. It has significant leverage with Syria as a result, and analysts in Baghdad believe that the Syrian raids would not have gone ahead unless they had been coordinated with Iran and Iraq.

Iran has a vital interest in ensuring that both Damascus and Baghdad remain within its orbit and has framed Syria's civil war and the grave threat to Iraq as the same conflict. Maliki has held the same view throughout the Syrian war and, despite his previous dislike for Assad, has allowed Iraqi air space to be used by Iranian military transport aircraft, whichregularly fly arms to Damascus.

Elsewhere in the country, Iraqi forces launched an airborne raid into Tikrit on Thursday, with helicopters disgorging soldiers into the city's sports stadium, from where they are expected to launch counterattacks against Isis forces, which who continue to occupy the city.

Much of the country's military has fled its posts in the north and Iraqi troops have so far been unable, or unwilling, to take on Isis in its newly won strongholds.

Isis has consolidated its hold on the central province of Diyala, forcing Kurdish peshmerga troops out of towns in the north of the province and continuing to attack Iraqi forces and Shia irregulars massed to the south.

A series of explosions and mortar attacks in the restive area of Mahmudiya and Latifiya, south of the capital, have raised fears that the jihadists are trying to open another front. Remnants of Maliki's forces and Shia militias have drawn battle lines in Baquba to the north and Taji to the north-west of the city.

Meanwhile, Masoud Barzani, head of the Kurdistan regional government, arrived in Kirkuk on Thursday for the first time since peshmerga forces took control of the city from fleeing Iraqi forces.

The highly symbolic visit is seen in Baghdad as the Kurds laying claim to Kirkuk, a city they have historically coveted. Peshmerga forces were seen shoring up the city's defences.

The capitulation of Iraqis forces has changed the balance of power between Baghdad and the Kurdish north, but the significance of the shift remains overshadowed by the seemingly unstoppable momentum of the Isis advances.

The British foreign secretary, William Hague, arrived in Baghdad on Thursday to urge Maliki to form an inclusive administration to deal with the crisis, which he described as an "existential threat".

"The single most important factor that will determine whether or not Iraq overcomes this challenge is political unity," Hague said, echoing the sentiments of the US secretary of state, John Kerry, who made the same call earlier in the week.

Maliki appears to have ignored both men, insisting that he will not form a government of national salvation with rival sects and leaders, because it would be "unconstitutional".

He remains under intense pressure to form a government by the time parliament is convened on 4 July, but seems unable to muster the support he needs to do so.