"I understand that police confronted with situations of difficulty do have to make judgement calls about how they will respond," she told a press conference.
"Whether it's on Christmas Island or whether it's in the CBD (central business district) of one of our capital cities on a Saturday night, police have to make those judgement calls.
"So I am not going to seek to stand here and second-guess those judgement calls."
Gillard said the consistent message from the government was that protests would not make any difference to the processing of claims.
"We ask people who are being detained to obey lawful instructions that are given to them, including instructions by police," she said.
Immigration Minister Chris Bowen earlier revealed that as well as tear gas, "bean-bag bullets" were used to quell protests on Monday.
"I have confirmed that they used gas and also they have confirmed that they used what's known as a bean-bag bullet," he said.
"I needed some education as to what a bean-bag bullet is. But as has been explained to me, it’s a bullet which the worst damage that can be done is bruising; it's like a little mini bean-bag which comes out of a gun-like weapon."More than 6,500 refugees -- mostly from Iraq, Afghanistan and Sri Lanka -- arrived in Australia last year on boats from Indonesia, crowding centres to capacity and inflaming debate on Canberra's tough mandatory detention policy.