Somalia on Wednesday threatened to withdraw from a grouping of East African nations after the bloc ruled in favour of Kenya in a diplomatic spat between the neighbouring countries, which have an often-fraught relationship.

Somalia severed diplomatic ties with Kenya on December 15 after alleging its larger neighbour was meddling in its affairs. Nairobi denied any wrongdoing, accusing Mogadishu of seeking a scapegoat for its own problems.

Leaders from the Intergovernmental Authority on Development (IGAD) regional group tasked a fact-finding mission with investigating Somalia's complaints that Kenya was violating its sovereignty, in an intervention aimed at easing tensions.

The foreign ministries of both countries said separately Wednesday that the inquiry had rejected Somalia's complaint, further angering Mogadishu, which accused the group of bias.

"IGAD has overwhelmingly demonstrated incapability to be a fair and independent arbiter," Somalia's foreign ministry said of the trade bloc comprising Kenya, Somalia, Sudan, South Sudan, Djibouti, Ethiopia, Eritrea and Uganda.

"The Federal Government of Somalia calls for immediate withdrawal of the baseless and unfair report and demands an apology, failure to which Somalia is considering withdrawing from IGAD."

Somali officials did not point to specific grievances for the decision to break off diplomatic relations in December.

But the announcement followed months of rising tensions, and came as Kenya hosted the leadership of Somaliland, a breakaway state not recognised by Mogadishu, which considers the northern region part of Somalia.

Mogadishu has also long resented what it believes is Nairobi's support for the semi-autonomous Somali state of Jubaland, which Kenya sees a buffer between it and Al-Shabaab militants over the border.

This week, at least nine people were killed in fighting in Jubaland that Somalia blamed on Kenyan troops and militias backed by Nairobi.

Kenya denied any role in the clashes, and has accused Somalia of stirring up diplomatic trouble to patch over its own internal political crises.

Parliamentary and presidential elections in Somalia slated for early February are well behind schedule, with political disagreements between the central and regional governments delaying a vote.

"The report of the fact-finding mission affirms the fact that allegations by Somalia against Kenya are wholly unfounded," Kenya's foreign ministry said in a statement.

"It is also clear that the decision by the Federal Government of Somalia to sever diplomatic relations with Kenya was uncalled for" and had negative repercussions for the African Union's AMISOM peacekeeping mission fighting Al-Shabaab.

Kenya is a major contributor of troops to AMISOM.

For its part, Kenya last year accused Somali troops of crossing the border into its territory during clashes with troops loyal to Jubaland.

Kenya also recalled its ambassador from Mogadishu in February 2019 in a long-running dispute over a stretch of the Indian Ocean claimed by both nations and believed to hold valuable deposits of oil and gas. The matter is before the international court.