John Kerin and Tracy Sutherland – The Prime Minister has faced a party-room backlash over planned migration zone changes designed to discourage Papuan asylum seekers, as three more were intercepted on a small island in the Torres Strait.

In an at times heated debate, up to 16 people spoke about the government's plans to introduce legislation next week that would mean anyone who arrives illegally by boat would be sent to offshore detention centres. Under the changes, asylum seekers landing on the mainland would be sent to centres in Nauru or Papua New Guinea's Manus Island.

At least five Liberal MPs spoke against the bill, including one who opposed it outright. The revolt was led by Liberal backbencher Petro Georgiou, who was understood to be concerned the changes meant the party was going back on hard-won concessions made last year that ended the detention of women and children.

"The sort of comment was, 'I cannot support this bill'," a party spokesman said. He said Mr Howard was willing to discuss the bill, but not to change its basic tenets.

Earlier, Mr Howard told the party room Australia had to handle the rift with Jakarta very carefully or risk the Balkanisation, or break-up, of Indonesia.

Labor's immigration spokesman, Tony Burke, who accused the government of kowtowing to Indonesia when it flagged the changes, said yesterday the government had not thought the plan through.

"This was the wrong position to take... it only takes one government senator to cross the floor and this legislation can be stopped," Mr Burke said.

The three Indonesians were in detention after being found at Boigu Island, Immigration Minister Amanda Vanstone said. "The three men, who had travelled on a small, unpowered native boat, were intercepted by immigration officials at Boigu Island on May 6," she said.

"Early indications are that they arrived from Papua New Guinea after having previously crossed from the Papua province of Indonesia."

As Boigu was one of the thousands of islands excised from Australia's migration zone last year, the three had been classified as offshore entry people, she said. If they sought protection, they would not be processed in Australia and were not entitled to make an application under the Migration Act. "They are currently on Horn Island and are in good health," she said.

The decision this year to grant temporary protection visas to 42 of the 43 Papuans sparked a row with Jakarta, which recalled its ambassador and accused the government of giving support to the troubled province's pro-independence movement, which the government denied.

Indonesian President Susilo Bambang Yudhoyono promised the Papuans would be free of persecution if they were returned. But Australia granted them three-year protection visas.