WASHINGTON (Reuters) - Health insurer Anthem Inc (>> Anthem Inc) denied a report on Thursday that it was in negotiations with the Justice Department in an effort to save its merger with smaller rival Cigna Corp (>> CIGNA Corporation).

Cigna shares jumped as much as 2.4 percent early in the session on a spike in trading volume to hit their highest level since July 2015. Anthem was last up 1.3 percent to $168.95. Cigna was up 2.3 percent at $155.50.

The companies are awaiting a decision from a federal appeals court, which had been asked to rule on whether the Justice Department could stop the $54 billion merger on antitrust grounds. The lawsuit was originally brought by the Obama administration and a federal judge agreed that the deal should be stopped.

Asked about a report from CTFN, a service specializing in merger news, that Anthem was in talks with the Justice Department, spokeswoman Bonnie Jacobs said in an email: "Not accurate."

The Justice Department declined to comment.

An Anthem purchase of Cigna would create the largest U.S. health insurer. Rivals Aetna Inc (>> Aetna Inc) and Humana Inc (>> Humana Inc) had also sought to merge, but that deal collapsed amid opposition from the federal government and states.

Adding to obstacles facing a deal, Anthem and Cigna, which have had difficult relations for months, are suing each other.

(Reporting by Diane Bartz and Rodrigo Campos; Editing by Dan Grebler)

Stocks treated in this article : Aetna Inc, CIGNA Corporation, Humana Inc, Anthem Inc