By defence correspondent Jonathan Marcus

The New York-based Human Rights Watch has called on the Russian military to stop using fuel air explosives, known as vacuum bombs, in Chechnya.

In an open letter to acting Russian President Vladimir Putin, Human Rights Watch said the explosives were a highly destructive weapon that risked significant civilian casualties.

The organisation also expressed its profound concern about the large number of civilian casualties caused by what it calls "the widespread and often indiscriminate bombing and shelling by Russian forces" in Grozny and elsewhere.

Influential

Human Rights Watch is an influential group with proven military expertise.

It recently released a highly critical report on Nato's air operation against Yugoslavia.

Now it has turned its attention to the Russian armed forces' performance in Chechnya.

It draws particular attention to the Russians use of fuel air explosives.

A typical bomb consists of a container of fuel and two separate explosive charges.

After the munition is dropped or fired the first explosive charge breaks open the container at a pre-determined height dispersing the fuel as a fine mist over a large area.

This mist mixes with atmospheric oxygen and flows into and around structures.

The second charge then detonates the cloud creating a massive blast wave. This pressure wave kills people even in cellars or bunkers.

If people are not killed by the blast they are incinerated.

The Russian military has consistently denied using such weapons.

But Human Rights Watch believes there is sufficient evidence of their use in both the Grozny suburbs and now in southern Chechnya for it to voice its concerns.