Previously, the US had insisted on only selling arms to the Iraqi government in Baghdad, but the Kurdish peshmerga fighters had been losing ground to Islamic State militants in recent weeks.
The officials wouldn't say which US agency is providing the arms or what weapons are being sent, but one official said it isn't the Pentagon. The CIA has historically done similar quiet arming operations.
The officials spoke on condition of anonymity because they were not authorized to discuss the operation publicly.
The move to directly aid the Kurds underscores the level of US concern about the Islamic State militants' gains in the north, and reflects the persistent administration view that the Iraqis must take the necessary steps to solve their own security problems.
To bolster that effort, the administration is also very close to approving plans for the Pentagon to arm the Kurds, a senior official said. In recent days, the US military has been helping facilitate weapons deliveries from the Iraqis to the Kurds, providing logistic assistance and transportation to the north.
The State Department sought to downplay the significance of the apparent shift in US policy.
The militants have "obtained some heavy weaponry, and the Kurds need additional arms and we're providing those — there's nothing new here," said department spokeswoman Jen Psaki.
She said the US was working with Baghdad to speed up deliveries of "badly needed arms" to Kurdish forces in the north. The Iraqi government, she said, "has made deliveries from its own stocks and we are working to do the same."
The additional assistance comes as Kurdish forces on Sunday took back two towns from the Islamic insurgents, aided in part by US airstrikes in the region. President Barack Obama authorized the airstrikes to protect US interests and personnel in the region, including at facilities in Irbil, as well as Yazidi refugees fleeing militants.
US Defense Secretary Chuck Hagel, speaking to reporters here, said the airstrikes "have been very effective from all the reports that we've received on the ground." He declined to detail how or when the US might expand its assistance to Iraq, or if military assessment teams currently in Baghdad would be moving to a more active role advising the Iraqi forces.
"We're going to continue to support the Iraqi security forces in every way that we can as they request assistance there," Hagel said during a press conference with Australian Defense Minister David Johnston.
At the same time, the administration is watching carefully as a political crisis brews in Baghdad, and US Secretary of State John Kerry warned Iraq's embattled prime minister Nouri al-Maliki to maintain calm among the upheaval.
"We believe that the government formation process is critical in terms of sustaining the stability and calm in Iraq," Kerry said. "And our hope is that Mr. Maliki will not stir those waters."
Speaking in Australia on Monday, Kerry said there should be no use of force by political factions as Iraq struggles form a government. He said the people of Iraq have made clear their desire for change and that the country's new president is acting appropriately despite claims of malfeasance by al-Maliki.
Maliki is resisting calls to step down and says he'll file a complaint against the president for not naming him prime minister.
Kerry noted that Maliki's Shia bloc has put forward three other candidates for the prime minister job and says the US stands with the new president, Fouad Massoum.
Maliki has accused Massoum of violating the constitution because he has not yet named a prime minister from the country's largest parliamentary faction, missing a Sunday deadline.
Hagel and Kerry are in Sydney for an annual meeting with Australian defense and diplomatic leaders.