On Friday i was standing on a market street in Burj al-Barajneh in Beirut -- it's the suburb in the south of the city where ISIS had just detonated a series of suicide bombs.

Some 50 people were there -- soldiers, Hezbollah militants, police, government investigators -- all looking at the bomb site, all gathering information to help their investigation into how and why this busy market had become such a scene of carnage.

I'd been at a restaurant in downtown Beirut, having dinner, when I heard about the blasts -- I didn't realise at the time that it was a significant attack, and so later, when I heard about the number of dead, I jumped in a taxi with a Lebanese friend of mine and we went to the site.

There were a million people to get past before we could reach the street -- all were heavily armed with semi-automatic weapons. All wanted to know who I worked for and when I said New Zealand, for whatever reason, they let me through the cordon.

Up at the blast site, a soldier approached me and dropped something in my hand. It was late at night -- about 10 o'clock and I couldn't quite make out what it was. But under a street light i could see that it was a ball-bearing. The suicide vests had been stuffed with the bearings and when the vests had exploded, thousands of these small, glistening ball-bearings had ripped the life out of more than 40 people and injured close to 200.

A local approached me and said he wanted to show me some images on his phone -- they were images taken just after the bomb had been detonated. They are images I will struggle to remove from my memory, I think. There was an image of what was left of the suicide bomber, and the innocents killed in the attack -- women, children, just carnage.

I was in London during the July 7th bombings, I've seen the impact of terrorist attacks in Afghanistan too -- but on that street on Friday, right in front of me, was the the tangible sight and smell of terrorism. The tangible sight and smell of an ideology that left unchecked, has emerged into the greatest threat to public and national security in living memory.

The following day, as I boarded my flight home, news alerts began to pop up on my phone about reports of an attack in Paris.

I'd arrived in Beirut amid news of the Russian plane being downed in Egypt, then there was the suicide attack in Baghdad that targeted Shia and killed 26. Then Beirut -- another attack on Shia muslims. And now Paris. And it begs the question, who's next?

But the bigger question is -- and the most important question is -- how do you stop this? And can you stop it?

What we do know, I think, is that we can no longer do nothing.

Do nothing, and ideologies spread. Remember, ISIS began in Iraq. The group has amassed huge wealth from the oil refineries it now controls. It also controls every entry point into Syria. The group is up on the Lebanese border. Sympathisers have attacked Turkey. ISIS is trying to get inside Kurdistan. And so it goes on.

So how do you stop it? Left unchecked, we now have an enormous problem on our hands.

The Arab world should take the lead on this -- but what chance of that? What chance of the Saudis and the Iranians standing on the same side and denouncing ISIS -- of urging the disenfranchised and the dispossessed to seek an alternative to radicalism? Very little chance at all, I think.

But we can no longer do nothing.

There has to be a plan because at the moment, there is none.

At Burj al-Barajneh in Beirut on Friday, I saw blood on the streets. In Syria and Iraq, so much blood has been spilled already and suddenly, after the attacks on Paris, we have found ourselves all on the same side.

The very violence that millions of Syrians and Iraqis have been fleeing for five years, we are now all living in fear of that very same violence.

I don't know what the answer is, but I suspect it will begin with intensified air-strikes on Syria and Iraq -- but a way through this horror rests heavily on the shoulders of the UN Security Council.

It has a mandate to preserve life but it's failure to enforce a resolution on Syria has meant it is failing humanity on every front.