The office building of health insurer Anthem in seen in Los Angeles, California February 5, 2015. REUTERS/Gus Ruelas

WASHINGTON (Reuters) - Health insurer Anthem Inc ANTM.N 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 CI.N.

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 AET.N and Humana Inc HUM.N 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.