Dramatic evidence that America is involved in illegal mercenary operations in east Africa has emerged in a string of confidential emails seen by The Observer. The leaked communications between US private military companies suggest the CIA had knowledge of the plans to run covert military operations inside Somalia - against UN rulings - and they hint at involvement of British security firms.

The emails, dated June this year, reveal how US firms have been planning undercover missions in support of President Abdullahi Yusuf's transitional federal government - founded with UN backing in 2004 - against the Supreme Islamic Courts Council - a radical Muslim militia which took control of Mogadishu, the country's capital, also in June promising national unity under Sharia law.

Evidence of foreign involvement in the conflict would not only breach the UN arms embargo but could destabilise the entire region.

One email dated Friday, 16 June, is from Michele Ballarin, chief executive of Select Armor - a US military firm based in Virginia. Ballarin's email was sent to a number of individuals including Chris Farina of the Florida-based military company ATS Worldwide.

Ballarin said: 'Boys: Successful meeting with President Abdullay Yussef [sic] and his chief staff personnel in Nairobi, Kenya on Tuesday ... where he invited us to his private hotel suite flacked by security detail ... He has appointed is chief of presidential protocol as our go to during this phase.'

She refers to one 'closed-door meeting' with a senior UN figure and mentions there are 'a number of Brit security firms' also looking to get involved.

Ballarin claimed she has been given 'carte blanche' to use three bases in Somalia 'and the air access to reach them'.

She then suggests that the CIA have been kept informed of the plans. Ballarin states: 'My contact whom we discussed from the agency side requested an in-person meeting with me. I arrived in New York at 2340 last night and was driven to Virginia - arriving at 0200 today.'

According to the highly respected newsletter, Africa Confidential, which originally published extracts of the emails last week, Select Armor started its operation planning in Kampala, Uganda. The emails suggest that the Ugandan government were willing to help secure arms supplies for any operation although this is denied by security officials in Kampala.

In one reply to Ballarin, Farina said: 'A forced entry operation [into Mogadishu] at this point without the addition of follow-on forces who can capitalise on the momentum/initiative of the initial op will result in a replay of Dien Bien Phu'. This is a reference to the defeat of French colonial forces in Indochina in 1953.

The website of Farina's company ATS boasts it 'can execute operations in support of host national indigenous forces'. ATS claims it uses former US and British special operations personnel.

One email discussing funding of any operation sent from Farina to Ballarin states: 'We may have to re-focus our efforts in the US among the DOS [State Department] and DOD [Defence Department] to bring any forward movement to this effort.'

The Observer left several messages with both Select and ATS requesting interviews but nobody responded. Ballarin told Africa Confidential last week that the company's operations in Somalia were 'classified'.