Australian military jets could fly across the Syrian border to attack terrorist targets by the end of the week.

It took nearly a month for the Abbott government to come to a decision on the airstrikes, announcing on Wednesday they would go ahead.

The RAAF will target Islamic State forces in eastern Syria, avoiding the western conflict areas of Damascus and Aleppo.

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Defence force chief Air Chief Marshal Mark Binskin said they were looking for operations into Syria to start within the week.

“It depends on the tasking cycle and what targets may come up in the particular areas at the time,” he said.

Australia already has RAAF jets based in Dubai. They have been carrying out attacks against targets in Iraq since October 2014, with the Syrian airstrikes to take place across the border.

The legality of crossing sovereign borders

The conflict in Syria has seen about 11 million people displaced. Photo: Getty

But international law experts have questioned the legality of the air combat action.

Sydney University international law professor Ben Saul said targets would need to be carefully chosen to ensure no legal issues.

“Australia seems to be arguing, like the United States and Canada, that this is a case of the collective self defence of Iraq against cross-border attacks from ISIS based in Syria,” he told the ABC.

“I think there are real doubts about that legal claim, because ever since 1945 for a very long time it was always international law that you can only exercise force in self defence if one country has attacked another.”

‘This could go on for a number of years’

The Abbott govt announced the air strikes on Wednesday. Photo: Getty

Defence Minister Kevin Andrews said this extension of RAAF missions was a practical and logical extension of current operations over Iraq.

He told Channel 9 on Thursday morning the military action would be ongoing.

“Two or three years I can’t say in exact terms but the reality is this could go on for a number of years,” Mr Andrews said.

“With our coalition partners we believe we can make a real difference.”

An additional 12,000 permanent humanitarian visas were also announced on Wednesday.

The places would be a one-off offer to refugees in Syrian minorities and be on top of the 13,750 visas already offered in 2015.

– with AAP