The army chiefs of landlocked Ethiopia and the self-declared Republic of Somaliland have been discussing military co-operation as concern grows over a deal that could give Ethiopia a naval base on the Gulf of Aden.

The two sides signed a deal on 1 January to give Ethiopia commercial and military access to the sea.

Somalia called it an act of aggression.

It considers Somaliland as part of its territory and has vowed to defend its sovereignty.

Somaliland, a former British protectorate, seceded from Somalia in 1991 but is not internationally recognised as an independent state.

Ethiopia's Field Marshal Birhanu Jula spoke with Somaliland's Maj Gen Nuh Ismael Tani about "possible ways to work together" at a meeting on Monday in Addis Ababa, Ethiopia's military said in a statement.

No further details were given.

Somaliland agreed to lease part of the coast to Ethiopia for a naval base in the 1 January Memorandum of Understanding (MoU) that they signed, according to statements from both sides.

Somaliland has said that in exchange Ethiopia would agree to recognise it as independent at some point in the future.

Ethiopia has not confirmed this and instead talked about making "an in-depth assessment towards taking a position regarding the efforts of Somaliland to gain recognition".

Somalia sees the MoU as an assault on its territorial integrity. On Sunday, its President Hassan Sheikh Mohamud asked people to prepare for the defence of the country.

The African Union and the US have both moved to try and calm tensions.

Somalia's allies, including Egypt and Turkey, have pledged their support for Somalia.

As the military men from Ethiopia and Somaliland were meeting in Addis Ababa, Mr Mohamud was in Eritrea holding talks with his counterpart in Asmara, Isaias Afwerki.

Official statements made no direct mention of Ethiopia's deal with Somaliland, but it is likely that the issue came up.

Eritrea said the two leaders agreed to work together "with patience and constructive spirit while refraining from a re-active posture to various provocative agendas".

On Monday, President Mohamud's office said the two leaders would "discuss issues of mutual benefit".