ABUJA, Nigeria (AP) — U.S. reconnaissance aircraft flew over Nigeria in search of the nearly 300 kidnapped schoolgirls Tuesday, a day after the Boko Haram militant group released the first evidence that at least some of them are still alive and demanded that jailed fighters be swapped for their freedom.

A Nigerian government official said “all options” were open — including negotiations or a possible military operation with foreign help — in the effort to free the girls, who were shown fearful and huddled together dressed in gray Islamic veils as they sang Quranic verses under the guns of their captors in a video released Monday.