The conglomerate controlled by cable TV magnate John Malone said it bought 94.3 million shares in Sirius XM starting in the past week for $234.3 million, raising its stake to 48 percent.
It also said in a regulatory filing that it filed a new application with the Federal Communications Commission for consent to take control of Sirius XM. It said it plans to take more than 50 percent control of the New York-based company.
The FCC rejected Liberty's earlier application in May because it didn't establish that it intends to take actions that would give it full control.
Malone's Liberty saved Sirius XM from near-bankruptcy in February 2009 by agreeing to lend it up to $530 million in exchange for the preferred stock. Converting the stock would give it a 40 percent stake.
Last week, Liberty said it intends to spin off assets including Sirius into a separate company, separate from company that would hold its Starz pay TV channels.
The spin-off is expected to be tax free and is planned to be completed by the end of the year.
Neither company returned messages seeking comment.
Shares in XM rose 4 cents, or 1.6 percent, to $2.60 in after-hours trading after the filing was made. Shares in Liberty Media Corp., based in Englewood, Colo., rose 5 cents to $101.68 after hours.