A 25-year-old man climbed atop a water tank at Hasanpur area on Tuesday and threatened to commit suicide against the detention of 80-year-old Sikh activist Surat Singh Khalsa here.Amritpal Singh of Barnala district, who serves as priest in a Gurudwara, was coaxed to come down by the police and civil administration officials but in vain. The youth had attempted a similar act two days ago.The activist had been sitting on fast unto death here for three days demanding release of Sikh detainees lodged in various jails of the country who have completed their sentences.