Environment Secretary Owen Paterson said the chief veterinary officer has advised that the period of culling badgers should be extended in Gloucestershire.
In a written statement to Parliament, Mr Paterson said the cull has killed 708 of an estimated 2,350 badgers in the county - less than 30% of the total rather than the 70% that had been planned.
Mr Paterson said an application is being considered by Natural England.
He told the House of Commons that early indications showed the culls in both Gloucestershire and neighbouring Somerset were carried out in a "safe and humane" way, but demonstrated that "the cull period may need to be longer than six weeks in future".
As the prospect of gassing badgers to help control the spread of TB in cattle is raised in Parliament today, it brings back memories of the 1980s in Gloucestershire when the culling method was used, to the dismay of animal rights protesters.
Environment Secretary Owen Paterson faced further criticism today over the controversial cull of badgers in Somerset and Gloucestershire. One Labour MP called on him to resign after it was revealed that the culls might have to be extended because not enough animals had been shot.
Mr Paterson insisted the policy had been a success - but hinted that alternative methods were being looked at, as Bob Constantine reports.
The Environment Secretary Owen Paterson MP (Con, North Shropshire) has told the House of Commons that he will examine gassing as a means of culling badgers. It would only be used, he said, if it is proven to be 'safe, effective and humane.' Previously, badgers have been killed by shooting.