A US probe into a proposed $2.2bn (£1.1bn) buy-out of 3Com, a network equipment supplier, by a consortium involving a Chinese company is poised to enter a decisive second phase.

The Committee on Foreign Investment in the United States, a branch of the executive able to block sensitive inward investment, is this week expected to take the rare step of extending a month-long investigation into the deal by a further 45 days.