'The Heat' director Paul Feig says casting Sandra Bullock and Melissa McCarthy was ''all or nothing''.

The filmmaker - who previously helmed hit female comedy 'Bridesmaids' - insists he didn't want any other actresses to star in his new female cop comedy and was determined that they be cast in the lead roles.

He explained to ComingSoon.net: ''For me it was always them or nothing. When the script came to me I was told that Sandra was interested, so I was like, 'Awesome', because I wanted to work with her. And then Melissa and I had been trying to figure out something to do for a long time and the minute I read it, I was like, 'This is so great for her.'

''There was a moment where scheduling looked like it might not work out for either one of them and so the studio was like, 'Well, who else?' Honestly, there's plenty of women I love who I want to work with, but I was like, 'I don't know.' These two, for some reason... this combo feels like gold to me, and so we pushed it through.''

'The Heat' stars Bullock as straight-laced FBI agent Sarah Ashburn who is forced to team up with McCarthy's foul-mouthed police detective Shannon Mullins.

The comedy flick has been a huge success at the US box office, where it opened to $40 million last weekend, beating Channing Tatum's new movie 'White House Down'.