INDONESIAN police have deported the 24-year-old son of former Jemaah Islamiah (JI) leader Mas Selamat Kastari to Singapore, where he is being investigated for potential involvement in activities "inimical to the security of Singapore".

Indonesia's national police spokesman Ronny Sompie and Singapore's Ministry of Home Affairs (MHA) confirmed on Monday that Masyhadi Mas Selamat was deported last Wednesday (Oct 30), 10 days after his arrest in Solo, Central Java.

Masyhadi, who is known to the Indonesian police as Muhammad Hanif, was arrested just before his wedding reception. He reportedly had a fake identity card and had overstayed in Indonesia.

In a statement, MHA said a teenage Masyhadi and his family members went to Indonesia in 2002 to join Mas Selamat, who fled Singapore in December 2001 following police investigations into the JI network.

"Mas Selamat and his family had taken refuge in Indonesia with the assistance of the Indonesian JI network," the statement added.

It was unclear how many family members joined the JI leader in Indonesia. But MHA said Masyhadi stayed behind in Indonesia even after the other family members returned to Singapore upon Mas Selamat's arrest in 2003.

The ministry's statement added: "Masyhadi is presently under investigation to ascertain if he has been involved in activities that are inimical to the security of Singapore."

Mas Selamat, an Indonesia-born Singaporean, joined JI around 1990 but fled Singapore after the first wave of arrests of JI members in 2001.

While on the run, he plotted to hijack a plane from Bangkok and crash it into Changi Airport. But the plan was foiled.

He was arrested twice in Indonesia, in Bintan in 2003 and again in Malang in 2006, for carrying false identification papers. He was handed over to Singapore authorities in February 2006.

But he escaped from the Whitley Road Detention Centre in February 2008. He was captured in Johor in April 2009 and remains in custody in Singapore under the Internal Security Act.