Same-sex couples from the US state of New Mexico can get married in Massachusetts, state officials ruled this month, after determining that gay marriage had not been explicitly banned in New Mexico.

Massachusetts is the only US state to have legalised same-sex marriage. A gay rights group from the state asked officials to clarify the rules for out-of-state couples.

Along with Rhode Island, New Mexico is the only other US state that has not explicitly either banned or allowed same-sex unions.

Couples from both states can be granted marriage licenses in Massachusetts, although neither state has agreed to recognise the unions.

Gay rights groups in New Mexico say the ruling will help their campaign for domestic partnership rights.

Linda Siegle, lobbyist for campaigning group Equality New Mexico told the Boston Globe she knew of at least three New Mexico couples already married in Massachusetts.

“I think this decision is a sign of hope for the whole country,” she said.

“As more and more states get full equality and fairness for our people, it’s beneficial.”

In 2004, when same-sex marriage was introduced in Massachusetts, then-state Governor Mitt Romney prohibited out-of-state couples from getting married, citing a 1913 law which bars couples banned from marrying in their own states getting hitched in Massachusetts.

However, the marriages of more than 170 gay couples from New York were deemed valid because they happened before a 2006 ban on same-sex marriages in New York.

The states with civil or domestic union laws – California, Hawaii, Maine, New Jersey, Oregon, Washington and the District of Columbia, as well as the cities of New York and San Francisco – do not recognise gay marriages from Massachusetts.

In February, two attempts to ban same-sex marriage in New Mexico failed, and the issue is still being debated in Rhode Island.