By Jonathan Marcus BBC defence correspondent

The Turkish Government has officially agreed to take over command of the international security force in the Afghan capital, Kabul.

A cabinet statement said Turkey would assume command of the 5,000-strong force from Britain at a date to be decided after talks involving the United Nations.

The Turkish decision means the future of the UN-mandated force known as Isaf is assured - at least for the next six months.

However, the scope of the Isaf operation is unlikely to be extended beyond the immediate environs of Kabul.

Financial snags

When Britain agreed to assume command of the initial Isaf deployment last December, it did so on the basis that it would hand over command after about three months.

That has not proved to be the case.

Turkey is the only Muslim state contributing troops to the 18-nation force

Few countries seemed willing to take over as force commander, though Germany is now providing a subordinate headquarters at brigade level.

Turkey was interested in the overall command of the force, though hampered by cost considerations.

With American help these problems have now been resolved.

Turkey's role will not be open-ended, though its decision does assure Isaf's future for the bulk of this year, if, as is expected Isaf's existing UN mandate is extended.

Quite apart from offering Turkey some financial support, the United States also says it will maintain its practical assistance to Isaf as well.

Seeking stability

The US military provides logistical support; intelligence and also maintains a quick-reaction force to come to the aid of Isaf units if they get into trouble.

But speaking to reporters at Bagram airbase at the weekend, US Defence Secretary Donald Rumsfeld insisted that this was as far as American involvement in Isaf would go.

Many aid agencies and some Afghan officials have called for Isaf's role to be extended beyond Kabul.

There is no doubt that continuing instability in the country poses a major threat to the interim government.

But it has proved hard enough to muster a 5,000 strong security assistance force.

Getting troop contributions for a significantly larger peacekeeping deployment would be very difficult.

And without a sizeable US contribution, few other countries would be willing to take the risks.