Looks like a type of Rubus - raspberry/blackberry or if it is vining along the ground then a dewberry.

You may want to put your picture on the name that plant forum and mention that you're in Israel.

Only two Heracleum species occur in the British Isles afaik and they are easily distinguished by leaf shape, size and stem colour long before flowering. The jagged leaves and red stem on this one say giant to me.

Thank you, Annie, for that link! The shoots in their bottom photo look EXACTLY like these things when they sprouted up. Would you believe that since I posted this, the 3"-5" shoots are now 15-17" tall? No blooms of any kind yet though. But I vaguely recall planting a little 4" pot of balloon flowers (that later died off in our heat and the shady spot they were in) that was situated some 10' away from where these have cropped up, so maybe seeds off those were blown to this new location. I'm leaving it where it is for now and just enjoying it bolt higher and higher. :) @Roselee, I've never had any Blue Porter planted in my yard. But I have had some surprises sprout up that the master gardener that lived here before me might have had planted. It does look similar, but I think the balloon flower Annie mentioned is exactly what I've got, and I KNOW I had some of those situated nearby this spot last year.