Previously the US insisted on selling arms only to the Iraqi government, but that policy has changed now, senior US officials told AP.
The officials would not disclose what kinds of weapons are being supplied or which agency is funneling them.
One official said it was not the Pentagon. Historically, the CIA has been involved in the clandestine arming of foreign fighters in various conflicts.
Iraqi Kurds, who are engaged in intensive fighting with militants from the Islamic State militants, have been complaining that they are under-armed compared to the radical Islamists, who captured a lot of American weapons from the Iraqi army in a lightning offensive in June.
The Kurds earlier received arms deliveries from the Iraqi government, an unprecedented move for Baghdad, which in the past has been reluctant to further empower the semi-autonomous Iraqi Kurdistan. The deliveries were facilitated by the US.