Israeli troops clear Gaza areas 'slice by slice', but is this an invasion?

Israeli forces appear to be concentrating on the northern area of the Gaza Strip, in Beit Hanoun, and pushing down a bit further south from there.

I am in Sderot, the Israeli border town overlooking Gaza.

Continuous heavy artillery fire into Gaza continues.

The Israeli battery near here is firing several times a minute.

The town itself is almost deserted.

Most civilians have either left or been evacuated.

The Israeli army has said it is upping the tempo of operations.

We have seen from video that has emerged from Gaza on Saturday morning, and from what could be seen along the border area on Friday night, evidence of a very, very large bombardment.

But the communications blackout means it's very hard to find out exactly what's going on.

For example, I have spoken to the UN who have been able to communicate with their main office in the south over a satellite phone, but as there is no internal communication, they can't connect with their area offices that look after their aid operations - currently suspended completely - to see how they are doing.

While the bombardment is very focused on the north, the Gaza Strip is only about 45km long (28 miles), so you can hear the extent of the explosions for miles around and certainly throughout the area.

As I understand it, the Israeli army is most likely attempting to clear out tunnels, probably with special forces spotting targets for those air force attacks.

Tanks can be more vulnerable in daylight so they may pull some of those back.

But as far we can tell, it is still going on.

Is it a ground offensive? I don't think we should get too hung up on the definitions of all of this. When we saw the military build-up, the mobilisation of over 300,000 reservists, we thought we would be seeing an all-fronts invasion of Gaza.

I think what they may be doing, though, is clearing areas of Gaza slice by slice. I have felt from the tone of comments from the Israeli army that their emphasis was that they would continue pushing, and that this was about "payback".

I think you could call this a very extended raid, or a ground offensive. It is certainly a very large military operation.

Israel's push on the ground is certain also to be killing Palestinian civilians.

The more Palestinians they kill the greater the outrage elsewhere in the Middle East, in countries friendly to Israel as well as its enemies.

That doesn't guarantee the war will spread. But it increases volatility and uncertainty in a region that is already fragile.