Sienna Miller's friends won't ''rule out'' a reunion with Tom Sturridge.

The 'American Sniper' actress is believed to have split from the 29-year-old actor - with who she has three-year-old daughter Marlowe - after four years together but insiders don't think the relationship is definitely over for good.

A source said: ''They are over, but don't rule out a reunion.''

According to the insider, the couple - who got engaged in 2012 - separated because Tom was keen to expand their family further, but the 33-year-old actress, who was a member of the jury at this year's Cannes Film Festival, is currently focused on her career.

The source added to People magazine: ''Tom wanted to get married and have more children. Sienna didn't.

''This year everything exploded with Tom in London and Sienna leading a separate life in the U.S. and [her appearance at] Cannes.''

News of the split came just two months after the 'Sea of Trees' star was seen without her engagement ring while at Cannes, prompting rumours their relationship could be on the rocks following what friends described as a series of ''blazing rows''.

However, just last year, Sienna - who famously starred opposite her beau in a 2013 Burberry advertising campaign - gushed about Tom's soothing personality.

She said: ''He's the perfect balance to my lunacy, which makes him sounds really boring but he's not, at all.''