Image copyright Getty Images Image caption The court could effectively make gay marriage legal across the country

The US Supreme Court will rule this year on whether gay couples have a right to marry across all states.

The justices said they would hear a combined case about marriage bans in four states.

But a supreme court ruling on the cases could fully legalise gay marriage in the US.

The court previously struck down a US law preventing federal recognition of marriages in states allowing same-sex unions.

After that ruling, a wave of decisions in the regional federal appeals courts ended numerous state gay marriage bans.

Thirty-six states and the District of Columbia now issue marriage licences to same-sex couples. Fourteen state bans remain.

On Friday, the justices said they would take up cases from gay and lesbian plaintiffs in Kentucky, Michigan, Ohio and Tennessee.

Image copyright Getty Images Image caption Gay marriage supporters cheered the June 2013 ruling that struck down a law limiting recognition of the unions

In November, a US appeals court overturned rulings striking down marriage bans in those four states, the first appeals court to do so since the Supreme Court's initial gay marriage ruling.

The US high court previously declined to intervene in cases that had made it to the appeals court level, effectively allowing marriages to go forward.

During two-and-a-half hours of arguments, the justices will consider two related questions - whether the US constitution requires states to issue marriage licences to gay and lesbian couples and whether states must recognise such marriages performed in other states.

The case will be argued in April and a decision is expected by late June.