Comcast has announced to the Stock Exchange that it has already acquired 29.1 per cent of Sky shares, and intends to purchase more.
21st Century Fox still holds a 39 per cent stake in Sky and has said it is considering its options.
Comcast requires the backing of more than 50 per cent of Sky's shareholders to gain approval for its near £30 billion offer. The deadline for Sky shareholders to accept the offer is 11th October.
With the Sky takeover, Comcast will become the biggest pay-TV provider in the world, with around 52 million customers after adding Sky's 23 million subscribers.