The parents of two Palestinian siblings gunned down at a West Bank checkpoint say Israeli troops killed them without cause.

The deaths of 24-year-old Maram and her 16-year-old brother, Ibrahim Taha, raise new questions about Israel's use of lethal force against Palestinians with knives.

Sarit Michaeli of the Israeli rights group B'Tselem said Thursday that it often finds the "degree of threat posed by the individual was much lower than was claimed by security forces."

Israeli police says troops shot the Taha siblings on Wednesday after they ignored calls to stop and Maram threw a knife at a policeman.

Since September, 28 Israelis and two Americans have been killed by Palestinians, while some 200 Palestinians have been killed by Israelis, mostly in what Israel says were attacks or attempted attacks.