Washington DC city council has voted to recognise same-sex marriages conducted in other US states.
As Washington DC is not a state, the decision will now have to be approved by Congress before it can become law.
Four US states - Vermont, Connecticut, Massachusetts and Iowa - now permit gay marriage, and legislation to allow it is in progress in other states.
A bill allowing same-sex marriage in Maine is likely to be sent soon to the governor to decide whether to sign it.
On Wednesday, the Maine House of Representatives approved the legislation by 89 votes to 56. The measure will now go back before the State Senate, which is also expected to pass it before going to Democratic Governor John Baldacci.
Mr Baldacci, who has in the past opposed, gay marriage, has not made his intentions public.
In Washington DC, the city council voted 12 votes to one to pass the resolution recognising same-sex marriages performed elsewhere.
Council member David A Catania - one of two openly gay members of the body - explained his reasons for supporting the measure during the debate.
"This issue is whether or not our colleagues on a personal level view me and [Council member] Jim Graham as your equals," he said.
"If we are permitted the same rights and responsibilities and obligations as our colleagues. So this is personal. This is acknowledging our families as much as we acknowledge you."
Fellow council member, and former Washington DC Mayor Marion Barry, was the only member to vote against the proposal.
"I understand this is personal to you and Mr Graham," he said in response to Mr Catania's remarks.
"I resent Mr Catania saying either you are a bigot or against bigotry as though this particular legislation represents all of that."
The law will be sent to DC Mayor Adrian Fenty - a supporter of gay marriage - for approval, before being placed before Congress.