Iraq’s political class has watched with fear and envy in the last fortnight as American jets have slowed the Islamic State extremist group’s advance towards the Kurdish stronghold of Irbil.

At the same time the group, formerly known as Isis, has been trying to encircle Baghdad – untroubled by air strikes. Its manoeuvres near the national capital in recent days have consolidated gains it has made in the last two months and made the very existence of Iraq in its current borders ever more precarious.

With a new central government only three weeks from being sworn in, Iraqi leaders are imploring the US to honour what they perceived to be an implicit deal to protect Baghdad once an inclusive leadership was installed. They say support for only one side will guarantee the end of Iraq, allowing the insurgents menacing the capital to whittle away what is left of state control and terrorise large numbers of people into fleeing.

The officials, led at first by ousted leader Nouri al-Maliki, had said that only US air power could put a halt to Isis’s momentum. Iraq’s military had refused to fight the jihadists, surrendering large parts of the country as they advanced into Mosul and Tikrit and towards Kirkuk. They have been unable to reclaim lost ground and are struggling to defend oil and energy sites that are essential to Iraq’s viability. What remains of the Iraqi military is operating without US air cover. Kurdish forces, on the other hand, have taken comfort from air strikes that beat back Isis some 30 miles to the south-west of Irbil.

On Thursday, the jihadists staged attacks in an area 40 miles south of Baghdad labelled nine years ago by the US military as the “triangle of death”. Iraqi military officials say that area is next to impossible to defend without strategic weapons or US air support.

Iraq’s small, US-trained air force has been busy, but is unable to turn the tide against Isis. “We are hitting them 24 hours a day in Tel Keyf, Khazir, Shalalat and in Mosul,” said one pilot, a Kurd. “We do a lot of bombing, but our weapons are not good. Our best weapon is the Hellfire [missile]. The problem with Hellfire, it does not cause major damage, but it is good in terms of hitting the target. I fly a Cessna Caravan 202 which is designed for transport purposes but we have converted it into a bomber.”

He said Iranian air force pilots were active above Iraq. “I have seen with my own eyes that the Iranians have brought Sukhoi planes,” he said. “Everything in that unit is Iranian, including the pilot and the mechanics. They are in Rasheed base, a huge base south of Baghdad … the Iranians make barrel bombs and then use Antonov and Huey planes to drop them in Sunni areas. Some Iranian pilots have been shot down.

“When we go to bomb a place, the ground troops don’t accompany us. We bomb a place and kill a few, then Isis disperses, but they regroup later.” He said five helicopters had been brought down by the militants, while seven planes were set alight on an airfield in Tikrit.

As the war of attrition with Isis steadily tips in the militants’ favour, resentment is growing among influential Iraqis. “The American policy is shameful,” said Hassan al-Fayath, the dean of al-Nahrain University in Baghdad. “The Americans always say they are the leaders in fighting terrorism, but they didn’t lift a finger when Isis was taking parts of Iraq. The only time the Americans got involved was when they found it started threatening their interests by getting closer to the oilfields and to Irbil.

“Isis succeeded in securing Iraqi oil and now they have the resources to recruit more fighters and buy weapons. Why did everyone let them go that far and not intervene earlier?” He added: “Obama will launch more strikes to save the oil and his Kurdish friends.”

Issan al-Shimary, a political analyst, pointed out: “America said it won’t intervene unless the Iraqis manage to find a new prime minister and now this has happened. This will put more international pressure on Obama to be more involved in Iraq. American intervention is a must. It’s the most powerful country and they have the power to defeat Isis. I’m optimistic. I believe that Iraq will be a bridge to build communication between the US and Iran. It’s something both parties want to do.”

Saleh al-Obeidi, a spokesman for the influential Shia cleric Moqtadr al-Sadr, said: “Moqtadr approves [of] the US involvement in Iraq only if it is within the framework of an international rescue. But he doesn’t want a new American footprint in Iraq.”