The jury weighing evidence against Allen Stanford said on Monday it was unable to reach a verdict in the trial of the former Texas financier.

Stanford, on trial in federal court in Houston, is accused of running a $7.1 billion Ponzi scheme.

U.S. District Judge David Hittner called in the jurors and instructed them to keep deliberating, saying the trial had been costly in time and money. "I'm going to ask that you continue your deliberations," he said.

The jury has been deliberating for more than 20 hours. The trial began on Jan. 23.

It was not clear whether jurors had failed to reach a verdict on any of the 14 counts against Stanford, or whether they had failed to do so on just some of the counts. Failure to agree on all counts could result in a mistrial.

Hittner said if the jury again said it could not reach a verdict, he would ask whether it had reached agreement on any of the charges, which could lead to a partial verdict.