Natalie Portman credits Reese Witherspoon for her decision to join Instagram.

The 'Annihilation' actress admitted her friend has been a great ''support system'' in helping her adjust to modern life but admitted she hasn't yet properly got to grips with the photo-sharing social networking site.

She told 'Entertainment Tonight': ''Reese has been a wonderful support system in teaching me the ways of modernity. There's this thing called social media.

''It's a very new thing in my life, and I feel like a grandmother who's learned how to use the microwave. Wow, it heats things up!''

Shortly after Natalie began posting on Instagram on 1 January, Reese shared a photo of herself and her pal to highlight the latest addition to the site.

She captioned the image: ''This is a photo of me convincing @natalieportman to join @Instagram!! Welcome her to the Insta family, y'all! (sic)''

The 'Black Swan' actress - who has children Aleph, six, and Amalia, 11 months, with husband Benjamin Millepied - recently vowed she would never let herself be ''pitted against'' other female stars for leading roles.

Speaking about her work with the Time's Up anti-harassment initiative, she said: ''It's been really incredible to gather actresses because I think something that we realised was that we're usually the only woman at work. So like many other industries, we walk onto a nearly all-male set, and we're usually alone and we rarely get to interact with each other.

''[There's power in] just all being in a room together and sharing our experiences and realising how much we've been endangered by being isolated.

''We refuse to be pitted against each other. There's not only one spot. We're going to make room for all of us. It's really, really powerful and really incredible and we have all of these new friends.''