LONDON — Islamist opposition fighters in Syria, including members of an Al Qaeda affiliate, took control of the Quneitra crossing point on the demarcation line with the Israeli-occupied Golan Heights, activists said on Wednesday.

The move could bring Islamist forces within 200 yards of territory controlled by Israel. An activist in the area, contacted by Skype, said a coalition of Islamists, including members of the Qaeda-linked Nusra Front, opened an assault on the government-held crossing early Wednesday. The status of a United Nations force that is supposed to monitor the crossing point was unclear.

Militants with a rival and more extreme Sunni militant group, the Islamic State in Iraq and Syria, have spread from Syria into parts of northern and central Iraq.

The Israeli military said one soldier and an Israeli civilian were wounded by “errant fire” from the clashes at Quneitra on Wednesday, prompting an artillery barrage against two Syrian Army positions in the Golan Heights — the latest of several occasions when Syria’s civil war has spilled into Israel’s area of concern, prompting retaliation. Israel has said it has no interest in further involvement in the fighting.