Sydney, April 15 (IANS): The lawyer of "Bali Nine" gang members facing death sentence for trying to smuggle drugs into Indonesia in 2005 said on Wednesday that he would challenge in a constitutional court the clemency rejection by President Joko Widodo without giving any reason, a media report said.

"If I was in the shoes of Andrew Chan and Myuran Sukumaran I would want the right to know why my clemency had been rejected. This is not only for these two young men, it's for others who deserve to know the grounds. This is for the constitutional process in Indonesia. We have to give reasons. We have to make it more humane," said Todung Mulya Lubis, a prominent human rights lawyer.

He, however, said that constitutional court rulings were usually not retrospective and therefore would not directly affect Chan and Sukumaran's case, the Brisbane Times reported.

The lawyer said he had requested Attorney General H.M. Prasetyo to respect the legal process and not proceed with the executions until the outcome of the challenge was known, the daily said.

The execution of the two Australian convicts -- Andrew Chan and Myuran Sukumaran -- threatens to strain the diplomatic relation between Indonesia and Australia.

Australia has even offered to pay the costs of the convicts' life sentences in jail, if they are granted clemency.

Chan and Sukumaran have been transported from Bali to Indonesia's “execution island” of Nusakambangan, where they are to be killed by a firing squad.