The air campaign has entered its most intense phase yet.

With good weather expected to persist, Nato is looking to sustain an increased tempo of operations, which is now more than twice as high as it was at the beginning of the campaign.

There has been much criticism that, more than two months into the campaign, the destruction of a third of the Serbs' heavy weapons in Kosovo - as Nato claims - seems like a poor return for the more than 28,600 sorties - including over 8,000 actual bombing missions - flown so far.

Nato says it has also destroyed over 50% of Yugoslavia's frontline aircraft, and has attacked more than 2,000 targets, dropping around 15,000 bombs in all.

The alliance admits it got off to a slow start. In part that was the result of weather problems.

But senior military commanders have also complained that they were restricted by political considerations and the need to get the agreement of all 19 Nato members to their strategy.

Ideally, they would have struck much harder, sooner.

But now they believe they are putting real pressure on the Serb military. They have more than 1,000 aircraft now, compared to 350 or so at the beginning, and can attack from many different directions as new bases are opened in, for example, Hungary and Turkey.

And, despite criticism of targeting recently, they are also clearly attacking a broad range of strategic sites, as well as Serb forces directly.

Campaign questions

Nato commanders have argued that they must be allowed to press attacks home against the upper reaches of the Yugoslav command structure, to put pressure on the Yugoslav authorities.

Power lines have become a target

Attacks on the Yugoslav electricity distribution system are a case in point.

Nato says it is not targeting the Serb population directly, but it will not be disappointed that attacks on electricity distribution could cause civilian discontent, and certainly complicate things for the Serb authorities in setting priorities for power.

The debate in Nato is not whether the air campaign is proving effective, it is whether it will ultimately be enough on its own.

Many members hope that increased pressure from the air, plus activity on the diplomatic front, will force Belgrade to give in.

But others, notably the British, argue that there may only be a few weeks left for this strategy to work, before the alliance will have to confront the issue of whether it is prepared to mount at least a limited ground invasion of Kosovo.

Phase Three

In the meantime, the alliance has the option of intensifying the campaign further.

Ground troops remain a controversial topic

It has still not moved fully to what is known as Phase Three of the air campaign.

Phase Three would involve an even broader range of strategic targets throughout Yugoslavia.

Some of the targets being hit now have been taken from the original Phase Three list, for example the electricity distribution system.

But Nato is not at the moment hitting actual power stations. And there are a range of other targets for which commanders still have not been given clearance.

For some Nato countries, moving to Phase Three could be a tough decision.

Germany, for example, has expressed concerns about recent targeting mishaps, and some members of the German Government have suggested restricting targeting.