Scott Morrison in damage control in South Australia over submarine comments

As he prepares to formally trigger the federal election campaign within days, Morrison was forced into damage control on Thursday, reassuring South Australian voters about his support for domestic shipbuilding jobs.

South Australian federal Liberal MPs also said they expected the government to honour its commitment.

That was interpreted as a hint that a desire for shorter timeframes might trump local jobs when a decision is finalised early next year, and the issue was picked up by South Australian media outlets.

When the Aukus partnership with the US and the UK was announced in September, the three countries launched an 18-month study into how Australia could achieve delivery of at least eight nuclear-propelled submarines.

The Morrison government said at the time its intention was to build them in South Australia, although it never gave an iron-clad promise. It has yet to announce whether it prefers the US or the UK design, but has predicted the first submarines could be ready by the late 2030s.

The South Australian independent senator Rex Patrick and rival upper house contender Nick Xenophon both vowed to campaign to secure local jobs.

The government also faces renewed scrutiny over the cost of the abandoned French diesel-electric submarine project.

Defence officials told Senate estimates they expected the yet-to-be-completed settlement with French contractor Naval Group could be met from within the existing budget. About half of the $5.5bn in previously approved funding has already been spent.