GENEVA - India must not go ahead with the imminent execution of a professor convicted of charges related to bombing the All Indian Youth Congress in 1993, the International Commission of Jurists said on Thursday.

Devinder Pal Bhullar, a German-based Sikh, was sentenced to death in 2001 for masterminding the bombing, which killed nine people.

The bomb targeted Maninderjit Singh Bitta, a leader of the ruling Congress Party and a critic of militant separatists in Punjab.

India's Supreme Court rejected a plea to commute the sentence to life imprisonment in April this year and upheld its decision on August 14, the International Commission of Jurists, an international group of 60 lawyers and judges, said in a statement.

The International Commission of Jurists's South Asia Director Ben Schonveld said there were serious questions about Bhullar's trial.

"His conviction and death sentence are based solely upon an alleged confession he made in police custody, which he later retracted, claiming it was extracted under torture," Schonveld said in the statement.

In a separate statement, Amnesty International said one of the three judges at Bhullar's trial had found him not guilty, saying there was no evidence to convict him.

It also said international standards prohibited the use of the death penalty against people with mental disability, and Bhullar had reportedly been suffering from psychosis and severe depression and had suicidal tendencies.

India ended an eight-year moratorium on the death penalty in November 2012 with the hanging of Ajmal Kasab, the lone survivor of the alleged Mumbai assailants.

India also hanged Mohammad Afzal Guru in February this year for an attack on India's parliament in 2001.

The execution sparked clashes between protesters and police in Kashmir in which dozens were injured.