Conservative Prime Minister John Howard's federal government has invoked special powers to invalidate a territory's law that had been the first in Australia giving legal recognition to same-sex relationships.

The Australian Capital Territory, which includes the national capital Canberra, last month became the first of Australia's six states and two territories to legally recognize gay and lesbian relationships.

The new law established a domestic relationship — separate to marriage — under which same-sex couples were to be given the same rights as heterosexual partnerships.

Officials in Howard's center-right coalition — which amended federal marriage laws in 2004 to ensure that only men and women can marry — opposed the law, saying it effectively legalized gay marriage.

Attorney General Philip Ruddock said the government had used its power over territories — which have their own Parliaments and operate in a similar way to states — to invalidate the law. The authority is rarely used.

"The ACT civil relationships ordinance has been disallowed," Ruddock told reporters Tuesday.

"That means, in effect, that the legislative amendments introduced to establish a civil arrangement for same-sex parties and others in the ACT will no longer be law."