WASHINGTON (AP) — President Barack Obama is acknowledging that "civilians have been killed that shouldn't have been" in past U.S. drone strikes, but says the administration is now "very cautious" about taking strikes where women or children are present.

Asked at a news conference about an increase in the number of people targeted in several drone strikes against extremist targets in Libya, Syria and Somalia, Obama said the "legal architecture" around the use of drone strikes in the past hasn't been precise.

But in the last several years, he says, the administration has worked hard to prevent civilian deaths.

He says the U.S. has to take responsibility when it is not acting appropriately.