But they weren't. It was the French blowing up mines at the Serb roadblocks known as "Sierra 4" and the Stup Bridge - the two which for years have been the most difficult for UN aid convoys to get past.
When Nato troops moved in last week, they applied a fundamental principle in a way the UN never did. They established their authority and right to move freely straight away.
Croat, Serb and Muslim police looked on, sometimes sullen, sometimes bemused, as the Nato columns rolled by. The peace agreement, initialled at Dayton and signed in Paris, says the implementation force, I-For, will have unimpeded freedom of movement in Bosnia-Herzegovina. With that goes a moral authority the UN never had.
Establishing freedom of movement early was top priority. "It bedevilled the UN," said Major- General Mike Jackson, the commander of the British- led division which is responsible for the largest of the three Nato sectors. "Freedom of movement has to be absolute. We will take a pretty robust line."
The British 4th Armoured Brigade has already mounted two operations with armoured battle groups to ensure the roads to Banja Luka and Sanski Most are clear. On Thursday, even though only a few hundred of his troops had arrived, the commander of the US division based in Tuzla, Major-General William Nash, drove across the Serb-held Posavina corridor to the Sava bridge in the area of Brcko.
When Nato took over in Bosnia from the UN on Wednesday, it embarked on an operation without precedent not only in its own history, but in the history of peacekeeping. In nearly 50 years the Atlantic alliance has never mounted a real ground operation.
Now, some 60,000 troops are moving into Bosnia to implement an agreed peace. Yet traditional peace-keeping is not defined in the UN Charter - somewhat curiously, as it is the main activity with which UN white vehicles and blue berets were associated until the far more complex operation in Bosnia.
As it developed over the years, "traditional peace-keeping" came to mean keeping sides apart while negotiations continued. In Bosnia, the borders, zones of separation and timings have all been agreed. With luck Nato should not have too hard a time.
Local opposition could arise to the peace agreed by leaders of the two Bosnian sub-states, one Serb and the other Muslim-Croat. If so, Nato will deal with it harshly.
Unlike the UN, it is authorised to use force "to prevent interference with free movement or violence against civilians and refugees". The biggest problem is unlikely to be with the Serbs, who are war-weary and have tended to obey orders from their commanders, but with some of the Muslims.
The Muslim mujahedin include extremists from outside Bosnia. Under the Dayton agreement, these "foreign forces" must withdraw from Bosnia within 30 days of "D-Day" last Wednesday but checking up on them will be a problem.
About half the mujahedin are Bosnians, including men "ethnically cleansed" from Srebrenica or Zepa who are embittered and fanatical. In all, there are 2,000 mujahedin of Afghan or other foreign origin and 2,000 local.
The number of mujahedin swelled after the two eastern enclaves fell in July. A camp with about 1,000 mujahedin was established at the village of Pobrijezja, near Zenica. It is not always easy to tell the Afghans and Algerians apart from local fighters, and it will be difficult for the impoverished Bosnian government, with no transport of its own, to expel them.
Zenica lies in the US sector, which could cause extra problems as Islamic extremists tend to regard Americans as the No 1 enemy and the Americans feel much the same about them. "We will have to wait and see," a Nato officer said on Friday. "Moving them is the responsibility of the Bosnian Muslim army."
The Dayton agreement specifies that Nato troops will not go searching the countryside for war criminals, although if they run across them at a roadblock, for example, they will arrest them. In practice, General Ratko Mladic is still in charge of the Bosnian Serb forces behind the scenes, and Nato needs to tread warily until it has established itself.
It does not have the necessary means to check movements of the local population - nor does it want to. The Nato forces are awaiting precise instructions from the North Atlantic Council about what they should do with indicted war criminals if they capture any. Ultimately, those accused of war crimes are supposed to stand trial before a UN tribunal in The Hague.
After three days, the Nato operation seems to be running smoothly. When the whole force is there, in a couple of months, there will be 60,000 troops, with 60-ton tanks, artillery and attack helicopters. The Americans are sending a whole brigade of Apache helicopters and have 12 satellites over Bosnia to assist communications and reconnaissance. The question everyone is asking is: why did the world not do this three years ago?Reuse content