Prime Minister Tony Abbott has denied Fairfax Media reports that his government pushed the US to ask Australia to expand its RAAF air strikes against Islamic State jihadists to Syria.

“Senior government sources” told Fairfax Media on Wednesday the “driving force for the formal request… came more from Canberra – and in particular the Prime Minister’s office – than from Washington”.

But, on Wednesday, Mr Abbott denied these claims.

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“This was raised with me by the president in a conversation that the president initiated to discuss the Trans-Pacific Partnership trade negotiation, so it was raised with me by President Obama,” Mr Abbott said.

Earlier in the day, federal treasurer Joe Hockey had also denied the reports.

“I’m sure they’ve had many discussions about the issue from time to time but the fundamental point is the US made the request to us and we are considering that request,” Mr Hockey told ABC TV on Wednesday.

A decision will come in a week or so, Mr Abbott said on Tuesday.

Meanwhile, former Labor foreign minister Bob Carr says Australia has a moral obligation to accept the US invitation.

“The West has really got a moral obligation to act where it can be argued there’s a chance of saving civilian populations from the mass atrocity crimes that seem to follow very quickly when ISIS takes control of territory,” he told ABC radio.

If Australia does bomb Syria, any air strikes would be directed solely at Islamic State terrorists in Syria’s east, not near the capital Damascus or the country’s west, Defence Minister Kevin Andrews told Sky News on Tuesday.

Opposition Leader Bill Shorten, who was briefed on the proposal on Monday, said the decision should not be rushed.