According to media reports, US decided to take this step following Pakistan's inability to take action against terror groups, especially al qaeda and Taliban.
"The US was prepared to take unilateral action to expand Predator drone attacks beyond the tribal areas and, if needed, to resume raids by Special Operations forces into the country against al qaeda and Taliban leaders," a report said.
US official said that Obama's decision was briefed to Pakistan during US national security adviser Gen James Jones and John O Brennan, the White House counter terrorism chief, visit to Pakistan in Nov 2009.
However, US official said that the message was not an ultimatum but a measure taken to nudge Pakistan to pursue Taliban militants in Pakistan who are engaged in terrorists activities in Afghanistan.
Reacting to the decision, Pakistan officials said, " Jones's message was if Pakistani help wasn't forthcoming, the United States would have to do it themselves."
Earlier, Obama warned Pakistan to stop its ambiguous relation with militants in a two page letter written to president Asif Ali Zardari.