The Australian navy is believed to be dealing with an asylum-seeker boat off the WA coast that refugee advocates claim has women and children on board.

Oil and gas workers spotted the vessel at first light on Monday, about 140km off the Dampier coast.

The federal government has remained tight-lipped on the matter, with Prime Minister Tony Abbott insisting on Tuesday that it was the “iron law” of his government not to discuss on-water operational matters.

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“We do not discuss things in ways which would give comfort to the people smugglers,” Mr Abbott said in Canberra on Tuesday.

But WA Premier Colin Barnett said he understood the navy had stepped in that morning.

“The state police boat has been assisting the commonwealth – I think their role is pretty well complete now and the commonwealth naval vessels will take over,” Mr Barnett said in Perth.

“The state always assists in these sorts of operations … particularly when they come that far down the coast.”

Meanwhile, the Refugee Action Coalition claims women and children are on board the vessel.

“There definitely are women and children on the boat,” spokesman Ian Rintoul told AAP.

Mr Rintoul said the people on the vessel had made contact with the Vietnamese community and were seeking legal advice regarding any challenge that could be launched if authorities sought to return them.

“Discussions are happening now,” he said.

In April, a group of 46 Vietnamese asylum seekers were returned to their country after being secretly detained at sea for a month.

“Given the history … I think it’s very clear that they will hold them on the high seas, screen them out and attempt to directly return them,” Mr Rintoul said.

He said the boat “came close” to territorial waters, but is actually in the contiguous zone.