March 24 (Reuters) - A federal judge on Thursday gave Volkswagen AG and U.S. regulators until April 21 to reach a diesel emissions settlement covering about 600,000 vehicles following the automaker’s massive emissions cheating scandal.

U.S. District Judge Charles Breyer, and lawyers for the Justice Department and VW, said at a court hearing in San Francisco that they were making progress in intensive negotiations, but issues remain and no settlement has been reached yet.

Breyer said the remedy could involve fixing the 580,000 vehicles on U.S. roads or buy backs and other options, but said he would not disclose any details of the ongoing talks.

If no deal is reached by April 21, Breyer said he would consider holding a trial on the issue this summer to address the vehicles that the U.S. Environmental Protection Agency says emit up to 40 times legally allowable pollution in real world driving.