A previously unknown militant group in Gaza says Egypt must release Palestinian prisoners in return for a diplomat it has kidnapped.
Mr al-Musali was taken close to the Egyptian mission in Gaza City
The al-Ahrar Brigades group said it would free Hussam al-Musali only if all Palestinians being held in Egyptian jails were released within 48 hours.
Foreigners are frequently kidnapped in Gaza but Mr al-Musali, Egypt's military attache, is the first diplomat.
His car was stopped in Gaza City while he was on his way to work on Thursday.
Leading Palestinian militant groups condemned the kidnapping as a "cowardly act" that threatened Palestinian relations with an important neighbour.
The al-Ahrar Brigades' statement was obtained by the al-Jazeera television channel in Gaza and its authenticity could not be independently verified.
The statement read: "We ask the Egyptian people, the diplomat's family and all human rights watchdogs to pressure the Egyptian government to free all Palestinian prisoners in Egypt.
"If Egypt does not heed this demand, it will bear sole responsibility for the tragic consequences."
It says Egypt is holding dozens of Palestinian prisoners. Cairo has yet to respond to the demand.
Mr al-Musali was taken in daylight close to the Egyptian mission in Gaza City after two gunmen shot out his vehicle's tyres.
The kidnapping was condemned by a spokesman for Hamas, the victorious party in last month's parliamentary elections. He expressed the group's "extreme indignation at this crime".
The Palestinian Authority interior ministry said the kidnappers would "be punished according to the law and strong measures will be taken to prevent similar acts from recurring".
A statement posted on a website affiliated to Islamic Jihad denounced the kidnapping and called for Mr al-Musali's immediate and unconditional release.
The group praised Egypt's role in the Palestinian territories and called for an "end to lawlessness and the kidnapping of foreigners and Arab friends".