After decades of instability just across its border, Kenya has sent columns of troops, with air support, into Somalia to clear out the Islamist organisation al-Shabaab. It is not clear how far they aim to go or for how long they intend to stay.

The stated intention of the Kenyan forces is to push to Kismayo, the major port in southern Somalia and a source of significant finance for al-Shabaab. Kenya's military has a good chance of achieving this. But getting to Kismayo is one thing, it is quite another to stay there and win a war against a dedicated insurgent campaign. Kenya has entered a highly volatile political environment and needs to be clear about its objectives – a drawn-out engagement will likely be bad for Kenya, bad for Somalia and have security implications for the UK as well.

This intervention is happening in the middle of a catastrophic famine and will cause serious disruption to an already underfunded and overstretched aid operation. Al-Shabaab's ineffective response to the famine has lost it crucial domestic support; the danger is that a foreign intervention may give it a chance to deflect the blame and galvanise flagging support. Ensuring humanitarian access should be a top priority for Kenyan forces and could serve to undermine al-Shabaab's propaganda.

Somalia's weak Transitional President has condemned Kenya's actions. But there is strong support from the Intergovernmental Authority on Development (IGAD), the regional security body, and Ugandan and Burundian troops are already in Mogadishu as part of an African Union mission to support the Transitional Federal Government (TFG).

Kenya, like its predecessors the US, the UN and Ethiopia, is unlikely to be able to impose a solution on Somalia but it is just possible that a short campaign hitting al-Shabaab's fund raising capacity could create space for Somali groups to mount a challenge. This would mean allowing Somali communities to decide how they wish to be governed, potentially including al-Shabaab.

Although Kenya's motives are understandable, this military intervention could have highly negative consequences. The onus now should be on finding space for Somali-led solutions.

Roger Middleton is a consultant researcher at Chatham House's Africa Programme