Pakistan has to prove it is sincere about working with India to counter terrorism, Prime Minister Manmohan Singh warned after police accused Islamabad of plotting blasts that killed nearly 200 commuters in Bombay. "Pakistan will have to walk the talk," to back up its promise to cooperate on terrorism, Manmohan told reporters Tuesday night. "Whatever has been discovered (by Bombay police), we shall share that information with Pakistan and test them on how sincere they are in carrying forward the commitment I and President (Pervez) Musharraf have underlined," Manmohan said on his plane trip home from South Africa.Bombay police chief A.N. Roy on Saturday publicly accused Pakistan's spy agency, the Inter Services Intelligence (ISI), of orchestrating the July attacks on trains that also wounded 800. Pakistan has pledged to take action if India produces evidence to show that ISI was involved in the Bombay bombings, but has denied any role in the attacks. India froze peace talks with Pakistan in the aftermath of the attacks but agreed to continue the dialogue after a meeting between Manmohan and Musharraf in Havana on Sept. 16.