WASHINGTON >> President Barack Obama announced in May 2013 that no lethal strike against a terrorist would be authorized without “near-certainty that no civilians will be killed or injured.”

But amid unconfirmed reports of civilian casualties, the White House said this week that U.S. bombing in Iraq and Syria is not being held to the near-certainty standard. And the Pentagon, hamstrung by limitations in intelligence gathering, has been unable to determine in many cases whether the casualty reports are true.

“We do take extreme caution and care in the conduct of these missions,” Rear Adm. John Kirby, the Pentagon’s press secretary, said. “But there’s risk in any military operation. There’s a special kind of risk when you do air operations.”

When Obama outlined his strategy to fight the Islamic State group earlier this month, he cited as parallels the limited U.S. counterterrorism campaigns in Yemen and Somalia, where American drone missile strikes have targeted al-Qaida-linked militants. Aides said he was also thinking of Pakistan but didn’t mention those strikes because drone killings there are entirely the work of an officially unacknowledged CIA operation.

But when it comes to civilian casualties, it has become clear that the targeted killing model that Obama has expanded and honed throughout his presidency does not apply to the more intensive military operation against the Islamic State and the Khorasan Group in Iraq and Syria.

According to the White House, the reason the near-certainty standard is not applicable turns on a fine point of international law — the theory that the U.S. is not involved in “active hostilities” in Yemen and Somalia, but is in Syria and Iraq. Such distinctions are controversial, given the frequency with which American bombs and bullets have flown in both countries.

A more practical reason is that the self-imposed rules on drone strikes against al-Qaida are simply too restrictive for a conventional military air campaign against the Islamic State group, which the U.S. says is both a terrorist group and an occupying army, and has ordered the Pentagon to destroy.

“It is much different in scope and complexity” than Yemen and Somalia, said Rep. Adam Schiff, D-Calif., an intelligence committee member. “I think it will be very hard to apply the very restrictive rules they put in place for other theaters.”

The drone attacks in Yemen, Somalia and Pakistan are carried out either by the CIA or, at times in Yemen and Somalia, the military’s Joint Special Operations Command. They employ Hellfire missiles, relatively small munitions designed to destroy people and vehicles.

In Iraq and Syria, the Air Force and Navy are using cruise missiles and conventional guided bombs to destroy buildings and other infrastructure that Hellfires can’t bring down. Allies, including Britain, France and Arab countries, are also using conventional bombs.

While most of the air strikes have been directed at the Islamic State group, the U.S. also used cruise missiles to attack the Syria headquarters of the Khorasan Group, an al-Qaida cell said to be plotting attacks on the West. Syrian opposition figures have said that one of those missiles went astray Sept. 23 and killed women and children in the village of Kafr Daryan near Aleppo.

All told, human rights groups have said that as many as two dozen civilians have been killed in U.S. and allied bombings in Iraq and Syria. The U.S. military says it hasn’t confirmed any civilian death but hasn’t ruled it out in every case, either.

White House spokeswoman Caitlin Hayden said the near-certainty standard was intended to apply “only when we take direct action outside areas of active hostilities.”

Military officials say they are taking great care to avoid civilian casualties in Iraq and Syria, consistent with international law. But international law does not require a near certainty that civilians won’t be harmed in military strikes. U.S. officials say harm to noncombatants is inevitable in a large bombing campaign –especially when the enemy is embedded in civilian areas.

Obama himself made that point in his 2013 speech, in the context of explaining why targeted drone campaigns are preferable to conventional war when it comes to counter terrorism.

“Conventional airpower or missiles are far less precise than drones and are likely to cause more civilian casualties and more local outrage,” the president said.

Pentagon spokesman Col. Steve Warren said this week that the U.S is relying mainly on intelligence-gathering technology such as satellites, drones and overhead surveillance flights to determine whether there have been civilian casualties.

As a result, “It’s much harder for us to be able to know for sure what it is we’re hitting, what it is we’re killing and what is collateral damage,” said Tom Lynch, a retired colonel and former adviser to the Joint Chiefs of Staff who is now a fellow at the National Defense University.

Warren acknowledged that the Pentagon could not say for sure that every person killed in the bombing of Iraq and Syria has been a combatant.

After the near-certainty standard was imposed on drone strikes in Pakistan and Yemen, the frequency of strikes dropped precipitously, and the use of so-called signature strikes — attacks aimed at large groups of armed men who fit the profile of militants but whose names were not all known to the CIA — was curtailed.

–Ken Dilanian / Associated Press