Greens have warned broadcaster STV they could still resort to legal action in a bid to be included in the Scottish general election TV leaders' debate.

The party issued the warning as it handed over a petition with more than 10,000 signatures to STV's headquarters in Glasgow.

It comes after the broadcaster confirmed it would screen a debate between First Minister and SNP leader Nicola Sturgeon, Scottish Labour leader Jim Murphy, Scottish Conservative leader Ruth Davidson and Willie Rennie, leader of the Scottish Liberal Democrats.

The clash, which will be broadcast live from the Assembly Rooms in Edinburgh, will take place on Tuesday April 7, exactly a month before the general election.

With the Greens left out, party co-convener Patrick Harvie said they could consult lawyers over a possible legal challenge.

Zara Kitson, the Scottish Green candidate for Glasgow North East, said: "The option of legal action remains open to us but we hope today's show of support prompts a rethink by STV."

Ms Sturgeon, Ms Davidson, Mr Murphy and Mr Rennie have already backed calls for the Greens - who have seen their membership north of the border swell to above 8,500 after last year's independence referendum - to be included in the leaders' debate.

STV has said that it would include all the major parties as defined by the broadcasting regulator Ofcom.

But Ms Kitson argued: "The huge support we've had from across Scotland, and across the political spectrum, shows that a broadcaster excluding the Scottish Greens is out of touch with its audience.

"TV debates remain an important part of our democracy and as we head towards an election like no other with an electorate more engaged than ever before, it's essential that voters get to hear a broad range of voices."