Up to 200 British military personnel could be deployed to West Africa to help train a regional intervention force for Mali, Downing Street has said, in a further deepening of the UK's involvement in the conflict to drive out Islamist militants.

The Prime Minister's official spokesman said the troops would be in addition to the up to 40 personnel that Britain is offering to contribute to a European Union training mission to build up the Malian army.

In addition, the UK has offered to supply a roll-on, roll-off ferry to help transport heavy equipment to the French intervention force currently spearheading the fight against the Islamist militants. It will also allow allies such as the United States to fly air-to-air refuelling missions from British airbases in support of the French operation.

However, the spokesman said that an offer to establish a joint Anglo-French logistics headquarters in Mali to organise supplies to the French force had not been taken up by Paris.

With around 90 UK personnel already committed in the region with the RAF Sentinel surveillance aircraft and two C-17 transport aircraft already operating in support of the French mission, it could take the numbers involved to more than 300.

However, the spokesman said David Cameron remained adamant that British troops would not be involved in combat operations against the militants. He said: "We have been very clear with everyone about our position of no combat role. That remains entirely unchanged."

The mission to train a West African force known as Afisma - which has been under consideration since late last year - was being discussed at a donor conference for Mali being organised by the African Union in the Ethiopian capital, Addis Ababa.

British personnel will be involved in training troops from Anglophone countries, such as Nigeria, which is expected to be one of the largest contributors to Afisma, which is slated to take over from the French once their mission is over.

"We think the right way to do this is for regionally-led forces to take the lead. The UK's role in supporting Afisma is to support that regionally-led capability," the spokesman said.

He said it was yet to be decided whether the personnel would be based in the countries of the forces they are training or in Mali itself. He said: "That is part of the discussions that are ongoing." However, he said the personnel taking part in the EU training mission would not be involved in force protection.