Somalia has cuts diplomatic ties with Guinea because it hosted the president of the self-declared republic of Somaliland.
Somaliland declared its independence from Somalia 18 years ago but Somalia has never recognised this.
Somalia now says that Guinea has violated its unity.
A statement by the foreign ministry said Guinea "accorded the protocols of a Head of State" to a "separatist movement in Somaliland".
President of the self-declared republic of Somaliland Muse Bihi Abdi received a red carpet reception earlier this week in Guinea.
The statement said Guinea had disregarded all "relevant resolutions of the UN and African consensus".
The countries did not have close relations so in reality this move may not change anything, but Somalia's government is sending a powerful diplomatic message, the BBC's Somali Service says.
No foreign government officially recognises Somaliland as a state but last week, Kenyan's foreign ministry had referred to Somaliland as a "country" in a controversial tweet.
Somalia's government summoned Kenya's ambassador to Mogadishu to explain the tweet.