U.S. military commanders in Afghanistan are pushing for an expansion of ground operations across the border into Pakistan's tribal areas, the New York Times reported Monday.

In an article published online, the report said the new proposal, which has not yet been approved by President Barack Obama, reflected U.S. growing frustration with Pakistan's failure to shut down militant sanctuaries in its tribal region bordering Afghanistan which gave insurgents free pass across the border.

The proposal "would escalate military activities inside Pakistan, where the movement of American forces has been largely prohibited because of fears of provoking a backlash," said the report.

America's clandestine war in Pakistan has for the most part been carried out by armed drones operated by the CIA.

"The decision to expand American military activity in Pakistan ... would amount to the opening of a new front in the nine-year-old war," said the report. "It would run the risk of angering a Pakistani government that has been an uneasy ally in the war in Afghanistan, particularly if it leads to civilian casualties or highly public confrontations."

However, "a renewed sense of urgency" to make progress in the Afghan war outweighed the concern over possible backlash from Pakistanis, as the deadline approaches for the Obama administration to begin withdrawing its forces from Afghanistan, the report noted.

Obama on Thursday released the administration's review of his Afghan war strategy that saw the deployment of 30,000 additional troops.

"While the momentum achieved by the Taliban in recent years has been arrested in much of the country and reversed in some key areas, these gains remain fragile and reversible," the review said. "Consolidating those gains will require that we make more progress with Pakistan to eliminate sanctuaries for violent extremist networks."