Sarawak's immigration authority will not release the travel ban list of opposition lawmakers and activists.

"We execute orders from the state authority," said its director Ken Leben, who did not elaborate further.

The department however confirmed that four individuals were detained this year, adding that the ban list was updated as recently as last week.

"We would advise that if you feel you might be an undesirable person in Sarawak, you should not come," said Ken.

Thus far, at least 37 opposition lawmakers, activists and academicians have been banned, including PKR vice-president Nurul Izzah , PKR secretary-general Rafizi Ramli and Amanah president Mohamad Sabu. Clare-Rewcastle Brown, editor of Sarawak Report , is also on the list.

Opposition lawmakers said travellers engaged in legitimate political activity were allowed in under Section 66 and 67 of the Immigration Act and are considering taking legal action.

Meanwhile, the department today also announced that it has detained 594 alien residents in an operation lasting since January. Most residents had no travel documents.