A gay couple are suing the US State Department after only one of their twin sons received US citizenship.

Elad and Andrew Dvash-Banks were shocked to learn that one of their twins, Ethan, had been denied the same rights as his brother, Aiden, because his biological father was an Israeli citizen.

The twins were born in Canada in 2016 via a US surrogate using donor eggs and sperm from both fathers. Aiden is the biological son of Andrew, a US citizen, while Ethan has the DNA of Elad, who is an Israeli citizen.

After the couple submitted the DNA results which proved who was the biological father of each boy, they received Aiden's passport and a letter notifying them that Ethan's application had been refused because his father was not an American citizen.

The couple, who married in 2010, have filed a federal lawsuit against the State Department seeking the same rights for Ethan as his brother. The plaintiffs argue that, although the twins were born in Canada, both siblings should be eligible for US citizenship as the surrogate mother was an American citizen.

"What we're trying to do is pursue justice for Ethan and correct a wrong that the State Department is continuing to pursue that might affect other couples," Elad told the Associated Press.

"The message is that you're not fully equal. Your family is less than other families," Andrew said. "My son has been wronged here by the government."

Ethan and Elad Dvash-Banks
Andrew and Elad Dvash-Banks are taking legal action after only one of their twin sons was recognised as a US citizen YouTube/ImmigrationEquality

LGBTQ immigrants rights group, Immigration Equality, which filed the case, said that children of US citizens were entitled to citizenship, even if one of the parents was foreign.

The organisation's executive director Aaron Morris said: "If a mother and father walk into a consulate and have a marriage certificate and birth certificate, they're never asked any questions about the biology of the child. But the converse is also true and every same-sex couple will be asked that."

The State Department refused to comment on the ongoing case but pointed out guidelines on its website which states that a biological connection to a US citizen is necessary for an offspring to be granted citizenship at birth.

Elad Dvash-Banks and twins
One of Andrew and Ethan Dvash-Banks' twins has been denied US citizenship because he has his biological father's Israeli DNA YouTube/ImmigrationEquality