Maina Kiai, the UN Special Rapporteur on the rights to freedom of peaceful assembly and association said on Tuesday that the charges against Salman, head of the opposition al-Wefaq movement, may be a result of his exercise of freedom of expression and dissenting views.
The UN official also demanded the Bahraini regime provide the international body with further information in relation to the judicial investigation against him.
The remarks by the senior UN official come days after five UN rights experts called on the Bahraini regime to free Salman, emphasizing that the charges against him "appear to stem from the government's dissatisfaction" with Salman's calls "for the establishment of a democratic regime and for government accountability."
The Office of the UN High Commissioner for Human Rights (OHCHR) has also called on the Manama regime to immediately release the al-Wefaq leader.
However, the authorities in the tiny Persian Gulf kingdom have not heeded international calls.
On Tuesday, the prosecution at an appeals court called for annulling Salman’s acquittal over 'plotting to overthrow' the regime, demanding a tougher sentence.
The court also rejected a request for bail by Salman's defense team and adjourned the case until October 14.
Al-Wefaq in a statement denounced the court's denial of bail for Salman. "Bahrain continues to turn its back on international calls to abolish trials that lack international standards of a fair trial."
Sheikh Salman was detained on December 28, 2014 on charges of attempting to overthrow the ruling Al Khalifa regime and collaboration with foreign powers. He has strongly denied the charges, emphasizing that he has been seeking reforms in the kingdom through peaceful means.
On June 16, a Bahraini court sentenced him to four years in prison on charges that included insulting the Bahraini Interior Ministry and inciting others to break the law. He was acquitted of seeking regime change.
Salman's detention sparked condemnation from the international community and rights groups.
Anti-regime protesters have been holding demonstrations on the streets of Bahrain since mid-February 2011, calling for the Al Khalifa family to relinquish power.
Bahrain's ongoing heavy-handed crackdown on peaceful demonstrations has left scores of people dead and hundreds injured.