Barack Obama has approved a new policy shift which allows the Central Intelligence Agency and the US military to launch drone attacks in Yemen when the identity of those who could be killed is not known, according to US media reports.

The Washington Post, quoting administration officials, said on Thursday that the US president approved the use of "signature" strikes this month.

It also said that the killing of an alleged al-Qaeda fighter earlier this week near the border to Yemen's Marib province was among the first attacks carried out under the new authority.

The shift in policy is said to mark a significant expansion of the drone war against what the US alleges to be a group affiliated with al-Qaeda which is located in Yemen.

The Wall Street Journal quotes US officials as saying that the amended policy includes targeting fighters whose names are not known but who are deemed to be "high-value terrorism targets, or threats to the US".