Britain is "closely monitoring" the takeover of UK defence technology firm Ultra Electronics by US-owned Cobham amid security concerns, the government said Tuesday.

Ultra last week agreed to a 2.6-billion pound ($3.6-billion, 3.0-billion-euro) takeover from Cobham, the former London-listed defence giant now owned by Advent.

US private equity group Advent has pledged to protect sensitive government information and keep Cobham's headquarters in Britain.

"While this is a commercial matter for the companies involved, we are closely monitoring the transaction," a government spokeswoman told AFP Tuesday.

Advent had agreed to buy Cobham in 2019 in a 4.0-billion pound deal approved by the UK government after a national security probe. That transaction completed early last year.

Cobham is known for pioneering technology enabling the mid-air refuelling of planes, while it also makes electronic warfare systems and communications for military vehicles.