Australia's parliament has voted narrowly to condemn a planned refugee swap with Malaysia, raising doubts whether the government will be able to carry through with the controversial plan.

The left-wing Greens party joined the conservative opposition to criticize the scheme, which would send 800 undocumented asylum seekers to be detained in Malaysia while their requests are processed. In return, Australia would accept 4,000 approved refugees from Malaysia.

Government officials insist the vote is not a fatal blow to the plan, which Canberra says would deter smugglers from bringing people on the hazardous journey to Australia in rickety boats. The Greens oppose sending any asylum seekers abroad, while the opposition coalition wants to reopen a detention camp in the remote Pacific island of Nauru.

Press reports say the government has also sent a delegation to Geneva to shore up support for the plan with the United Nations High Commissioner for Refugees. The agency has expressed concern that unaccompanied children might be sent to Malaysia under the plan.