Minister Hussein Mjali previously served as the defense lawyer of army Corp. Ahmed Daqamseh who shot dead the girls during an outing near Jordan's border with Israel.
Monday's protest outside Mjali's office was organized by Daqamseh's family. Mjali joined the protesters, saying he was participating in his capacity as the soldier's former lawyer. "I'm committed to be here with you as his lawyer," Mjali told the cheering group.
Israeli Embassy spokeswoman Merav Horsandi said it "is difficult for us to comprehend how there are people who support the release of a cold-blooded murderer of young children."
She said an early release would contradict the spirit of the 1994 peace treaty between the two countries. "Israel cannot imagine a situation in which such a vile murderer will be set free by the Jordan," she added.
The corporal was sentenced to life in prison, which translates into a 25-year sentence in Jordan. It's unlikely he will win early release.
Jordan maintains cordial ties with Israel. The peace treaty stipulates that both countries should refrain from actions that could incite tensions or harm diplomatic relations.
Mjali was appointed in a government shakeup last week in the wake of protests inspired by the Egyptian uprising. The protests ushered in a broad-based Cabinet pledging greater democratic freedoms, including the rights of assembly and speech.
Mjali said Monday he joined the Cabinet because he wants see greater freedom of speech in Jordan.
It was not immediately clear if his appearance at Monday's protest will have repercussions.
A government spokesman said the Cabinet didn't discuss the issue. "It's apparently the minister's own initiative and he has the right to express himself," added the spokesman, insisting on anonymity because of the sensitivity of the issue.
Mjali's boss is Prime Minister Marouf al-Bakhit, who served as Jordan's ambassador to Israel several years ago. He is a former army general who advocates close ties with the United States and Israel.