WASHINGTON — The Obama administration is turning up the pressure on Pakistan to fight the Taliban inside its borders, warning that if it does not act more aggressively, the United States will use considerably more force on the Pakistani side of the border to shut down Taliban attacks on U.S. forces in Afghanistan, U.S. and Pakistani officials said.

The blunt message was delivered in a tense encounter in Pakistan last month, before President Barack Obama announced his new war strategy, when Gen. James L. Jones, Obama's national security adviser, and John O. Brennan, the White House counterterrorism chief, met with the heads of Pakistan's military and its intelligence service.

U.S. officials said the message did not amount to an ultimatum, but rather it was intended to prod a reluctant Pakistani military to go after Taliban insurgents in Pakistan who are directing attacks in Afghanistan.

The Pakistanis interpreted the message as a fairly bald warning that unless Pakistan moved quickly to act against two Taliban groups they have so far refused to attack, America 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-Qaida and Taliban leaders.

One senior administration official, when asked about the encounter, declined to go into details. But he added quickly, "I think they read our intentions accurately."

A Pakistani official who has been briefed on the meetings said, "Jones' message was if that Pakistani help wasn't forthcoming, the United States would have to do it themselves."

The security demands followed an offer of a broader strategic relationship and expanded nonmilitary economic aid from the United States. Pakistan's politically weakened president, Asif Ali Zardari, replied in writing to a two-page letter that Jones delivered by hand from Obama. But Zardari gave no indication of how Pakistan would respond to the incentives, which were linked to the demands for greatly stepped-up counterterrorism actions.

"We've offered them a strategic choice," one administration official said, describing the private communications. "And we've heard back almost nothing."

The implicit threat of not only ratcheting up the drone strikes but also launching more covert American ground raids would mark a substantial escalation of the administration's counterterrorism campaign.

During his review of Pakistan and Afghanistan strategy, officials say, Obama concluded that no amount of additional troops in Afghanistan would succeed in their new mission if the Taliban could retreat over the Pakistani border to regroup and resupply.