Culture secretary Jeremy Wright said late on Monday that a review of the US$3.4bn take-private deal will be extended to include national security after his department received representations from the secretary of state for defence, the business secretary and the foreign secretary.
Last week, the Competition & Markets Authority brought the deal to the attention of the Secretary of State for Digital, Culture, Media & Sport as it may reduce competition in the market.
On Tuesday the CMA extended its invitation to interested parties to comment on not only the impact of the transaction on competition but also any public interest considerations, with responses due by 5 August.
Inmarsat in March agreed to be bought by a four-way consortium made up of private equity firms Apax Partners and Warburg Pincus, plus two Canadian pension plan boards.
On Monday, the UK Secretary of State for Culture, Media, & Sport, who has the power to intervene on national security grounds, issued a public interest intervention order.
New UK rules were introduced last year applying to takeovers by foreign companies, after concerns were raised that sensitive technology was being snaffed by foreign buyers.
The CMA will report to the government by 17 September, including any concerns over both national security or competition.
Inmarsat shares were down 1.4% to 554.6p on Tuesday morning.