Qantas is cutting domestic flights and increasing fare prices as the airline’s fuel bill is expected to soar by $800 million amid uncertainty over the Iran war.

The changes also impact subsidiary Jetstar, with customers of both airlines being offered alternative flights or refunds in May and June.

The cost of jet fuel has more than doubled since US-Israeli strikes on Iran began in late February.

There are fears of worse to come amid a US blockade of the Strait of Hormuz that has triggered more threats from Iran.

Qantas now expects to spend as much as $3.3 billion on jet fuel in the first half of its financial year, up from an original estimate of $2.5 billion.

Most of the airline group’s cuts will happen on key routes between capital cities which use larger aircraft at higher frequencies, a spokesperson said.

Where possible, Qantas will withdraw capacity at off-peak times to try to minimise the impact on customers.

Qantas and Jetstar customers with future bookings on cancelled flights are being contacted about alternative options or a refund.

Most of those affected will be offered other flights on the same day as their original booking, the airline said.

Qantas indefinitely cancelled all services to Mount Gambier in South Australia from May.

Routes that have been temporarily cut include:

• Melbourne and Hamilton Island , May 18 – June 28 (Qantas)
• Melbourne and Coffs Harbour, May 18 — June 28 (Qantas)
• Sydney and Busselton, May 18 – September 22 (Jetstar)
• Darwin and the Gold Coast, May 18 — October 12 (Jetstar)

Last month Jetstar said it was reducing flights between Australia and New Zealand — specifically between Auckland and Sydney and Brisbane — as well as domestic services in New Zealand.

Qantas is working with the government and jet fuel suppliers to ensure access to the commodity, although it expects no potential disruptions until well into May.

“We are closely monitoring the situation given the ongoing uncertainty in global fuel supply chains,” the airline said on Tuesday.

Given the volatility impacting prices and the global economy, Qantas will cut domestic capacity in the June quarter by around five percentage points.

Air New Zealand, Air India and Delta Airlines have also reduced capacity in recent days, citing surging jet fuel costs.

However, Qantas, which does not fly to the Middle East, is seeing more demand for international travel to Europe as customers seek alternative routes.

It is redeploying capacity from the US and its domestic network to increase flights to Paris and Rome.

Meanwhile, it has been confirmed that Australia would join an international summit on safeguarding shipping in the Strait of Hormuz.

Defence Industry Minister Pat Conroy said a coalition of nations was keen to find a diplomatic resolution of the conflict and for the strait to be reopened.

“The summit, from the UK and France, is obviously focused on how do we ensure safe passage for vessels. But we need peace first and we’ve been very clear about that,” he said.

“That’s why we need Iran and the United States to continue the ceasefire, return to negotiations so that the strait can be reopened.”

-with AAP