Jakarta – Jailed Indonesian labour leader Muchtar Pakpahan is being well treated by local doctors for an undiagnosed lung illness, a visiting Canadian specialist said on Wednesday.

"Up to the present time, as far as we can see, he is receiving optimal treatment here," Professor Stephen Lam told a news conference at Jakarta's Cikini Hospital.

Lam and two other Canadian doctors were due on Thursday to perform a highly sophisticated test on Pakpahan's right lung, where earlier tests revealed an unidentified object.

Pakpahan, 43, head of the independent and unrecognised Indonesian Labour Welfare Union (SBSI), is serving a four-year sentence for inciting riots, but was admitted to the hospital in March suffering vertigo.

U.S. and European unions had offered to pay for Pakpahan's treatment abroad but Indonesia rejected the request, saying his illness was not fatal.

The unionist is facing further charges of subversion that carry a possible death sentence, but the head of the Indonesian medical team Doctor Hermansyur Kartowisastro said a hearing set for Thursday morning would have to be postponed.