WikiLeaks cables, accessed by news channel NDTV, reveal Singh telling US Under-Secretary Nicholas Burns in Jun 2009 that he was having sleepless nights.
"If he, as PM, was talking peace while Pakistan territory was being used to plan terror attacks against India then he said he will be looking ridiculous in front of the Indian people," a WikiLeaks cable states.
Burns quotes Singh here as having told him during his visit to India.
Singh further informed Burns that he knew there are fresh threats and he "can't sleep well at night".
In another WikiLeaks cable dated Aug 11, 2009, then Indian National Security Advisor M K Narayanan, told US Ambassador to India, Timothy J Roemer, that he has differences with Prime Minister Singh on how to deal with Pakistan.
"The Prime Minister is a great believer in talks with Islamabad while he himself is not a great believer in Pakistan and is not enamoured by it," Roemer states.
Narayanan told Roemer that he also did not agree with Singh's belief in India having a "shared destiny" with Pakistan.
"I told the Prime Minister that you may be thinking of a shared destiny but I do not think so," Narayanan told Roemer.
The WikiLeaks cables also refer to Pakistan President Asif Ali Zardari's views about Prime Minister Singh. These views were expressed to US NSA, James Jones, on Jun30, 2009 in Islamabad.
"Singh is an excellent economist but I am not convinced that he understand my constraints," Zardari told Jones, in an apparent acceptance of how the Pakistan army held sway over the administration.
"Singh is unaware of what it took to change the mindset of the Pakistan establishment and how difficult it is to do so," Zardari said.
Jones reminds Zardari to ensure that no repeat of Mumbai-style terror attack should take place in India.