MUMBAI (Reuters) - Bollywood star Sanjay Dutt, convicted of keeping illegal arms and sentenced to six years, will have to surrender on Sept. 27 on expiry of his bail and will probably have to return to jail, a court official said on Monday.

The macho actor began serving his sentence on July 31 - for getting guns from gangsters linked with India's worst bombing that killed 257 people in Mumbai in 1993 - but was bailed last week after his lawyers petitioned the Supreme Court against his conviction and sought his release until that appeal was heard.

They said they could not argue the case as they were yet to get a copy of the judgement of the Mumbai court that sentenced Dutt.

The court agreed to release the actor until the lawyers got a copy of the verdict.

"He will be served a copy of the judgement on Sept. 27," V. Gawas, registrar of the special anti-terrorism court which tried Dutt and others accused in the attacks, told Reuters.

"He will have to surrender and go back to jail that day. That was the condition on which he was released."

Dutt is expected to be sent back to a jail in Pune where he spent more than three weeks before being released on bail on Aug. 23.

Dutt was among 100 people found guilty by the special court which had sentenced 12 people to death and 20 to life in prison while handing varied jail terms and fines to the rest.

Since coming out of jail, Dutt has mostly stayed home and, industry sources said, he is unlikely to resume shooting. He is acting in three films which are under production.