The Vietnamese property magnate detained in Singapore is being held for "committing offences under the Immigration Act", said the Immigration and Checkpoints Authority (ICA) yesterday.
An ICA spokesman also confirmed that Mr Phan Van Anh Vu, 42, was arrested on Dec 28.
The ICA did not respond to other queries on the case.
Its response follows news that Mr Vu, who is wanted in Vietnam for allegedly disclosing state secrets, was stopped from leaving Singapore via Tuas Checkpoint last Thursday.
One of Mr Vu's lawyers, Mr Choo Zheng Xi, said he filed an application with the Supreme Court yesterday requesting for Mr Vu to be given access to counsel.
Mr Choo told The Straits Times he also asked that Mr Vu not be sent back to Vietnam before the outcome of the application.
He also confirmed that Mr Vu is seeking asylum in Germany.
Mr Vu is said to have entered Singapore on Dec 21, but found himself unable to leave as his passport had been cancelled by the Vietnamese authorities, reported the BBC.
His whereabouts had been the subject of speculation in Vietnam, after the country's Ministry of Public Security said it issued an arrest warrant for him last month.
According to Vietnamese media reports, Mr Vu previously served as a police senior lieutenant-colonel.
He was also said to have close ties with former secretary of Da Nang Party Committee Nguyen Xuan Anh, who was also a member of the Communist Party of Vietnam Central Committee, according to a Xinhua news report on Dec 27.
Anh was dismissed from the two positions in October, according to the same report.
Mr Choo said the application he filed yesterday requested for Mr Vu to be given access to lawyers from his firm, as well as to Mr Foo Cheow Ming - another lawyer approached by Mr Vu's family to advise him.
When contacted, Mr Foo said: "We are now awaiting for the application to be heard and dealt with."
He added that Mr Vu remains in remand with the ICA, and he is "still trying to find out more from the arresting authorities".
Offences under the Immigration Act include remaining in Singapore unlawfully, for instance after the cancellation of a permit, and failing to present a valid foreign passport or travel document when entering or leaving Singapore.
Germany-based activist and blogger Bui Thanh Hieu also told The Straits Times Mr Vu was heading to Malaysia with a Vietnamese friend when they were stopped on Dec 28.
He added that he had learnt of this news from Mr Vu's friend, who was not detained.
The Saigon Times Daily reported in a Dec 25 article on its website that Mr Vu, who is a chairman of three companies in Vietnam, had been accused of deliberately giving away state secrets.
According to the report, police raided Mr Vu's residence in Da Nang city, but failed to find him there.
It did not elaborate on the nature of the state secrets.
The report also said Mr Vu is believed to be involved in some property projects being investigated by the police.
Singapore has no extradition treaty with Vietnam but under the Immigration Act, the ICA may repatriate people under certain circumstances.