Scarlett Johansson has today denied rumours she is pregnant with her first child.

The actress sparked speculation after she was pictured in Malibu over the weekend looking more curvaceous than usual.

The 26-year-old appeared to have a small bump protruding beneath her tight grey vest and black lycra leggings while on a run with her new boyfriend, Sean Penn, 50.

Working up a sweat: Scarlett Johansson, displaying a fuller figure than usual hit the pavement in Malibu with boyfriend Sean Penn

Rounder figure: Scarlett, 26, was sporting a noticeably rounded stomach during the jog

‘Scarlett is not pregnant,’ her spokesperson said in a statement today.

‘She’s outside running and it’s simply the placement of her shirt that is misleading’.

‘She’s been training for The Avengers for over four months and is in the best shape of her life.’

The pair were joined for the jog near Penn’s Malibu home by friend Owen Wilson, who puffed away behind the couple in a long sleeve T-shirt and shorts – the boys soon powered ahead though, leaving Scarlett trailing behind in their wake.

Three’s company: Scarlett and Sean were joined by Owen Wilson for the workout session

Scarlett and Sean, who have a 24-year age gap, were first linked together back in January, just weeks after she announced her divorce from her husband of two years, actor Ryan Reynolds.

They have been snapped together a couple of times and attended Reese Witherspoon’s intimate wedding in Ojai, California, last month.

The are said to have met at the Chateau Marmont in West Hollywood while Scarlett was filming We Bought A Zoo, her new movie alongside Matt Damon.

Voluptuous: Scarlett is known for her killer curves but was looking far more svelte in February at the Oscars

And Sean’s ex-girlfriend Jessica White gave the relationship her seal of approval in a rencet interview.

‘I think Sean needs a good woman in his life,’ Jessica told entertainment website Popeater.com. ‘They’re great together.’

Owen, Sean and Scarlett are all friends of director Woody Allen’s, though it is unclear if it was he who introduced them.

Scarlett is a muse to Allen and starred in three of his films, Match Point, Scoop and Vicky Christina Barcelona, while Owen stars in his latest, Midnight In Paris.

Wait for me! Owen and Sean powered ahead, leaving Scarlett (in background) far behind