Deputy Opposition Leader Julie Bishop has been forced to back away from comments in which she suggested Australian intelligence authorities had used forged passports.

Ms Bishop maintains the Government overreacted in deciding to expel an Israeli diplomat from Canberra over the use of forged Australian passports in the assassination of a Hamas leader.

She says it is naive to think Israel is the only country using forged passports in intelligence operations.

When she was asked if she believes Australia does, she replied yes.

"There is no actual proof that the Israeli government was involved," Ms Bishop said on Monday.

"There is an assumption. And in the absence of actual proof I believe that the expulsion of a diplomat is either an over-reaction or a calculated political decision.

"It would be naive to think that Israel is the only country in the world that has used forged passports, including Australian passports, for security operations."

But Ms Bishop has now issued a statement saying she did not state that Australian intelligence authorities have forged the passports of other nations.

She says she was referring to the fact forged Australian passports have previously been used.

The statement did not stop Prime Minister Kevin Rudd launching a scathing rebuke of Ms Bishop, accusing her of acting against the interests of national security.

He says there is a long-standing convention that neither side of politics comments on intelligence activities.

"Today that convention has been breached," he said.

"This is fundamentally contrary to Australia's national security interests."

Earlier in Question Time, Foreign Minister Stephen Smith said he was shocked by her statements and that she was not fit to occupy a position of trust.