AMMAN, Jordan — Jordan refused to release an imprisoned female militant on Thursday to meet a deadline set by the Islamic State, demanding that it first needed proof that a captured Jordanian pilot was still alive.

The impasse provoked fears that the extremists would carry out their threats to kill the pilot and a Japanese journalist they were also holding hostage.

Jordan said it had been prepared to meet the Islamic State’s demand to free the imprisoned militant, Sajida al-Rishawi, and deliver her to the Syrian-Turkish border by sunset on Thursday.

“Rishawi is still in Jordan, and the exchange will happen once we receive the proof of life we ask for,” Agence France-Presse quoted the minister of state for media affairs, Mohammed Al-Momani, as saying shortly before the deadline expired.