Ericsson has taken the unusual step of attacking Moody's Investors Service after the ratings agency downgraded the Swedish telecoms equipment manufacturer's credit rating by two notches, leaving it facing an extra Skr110m (€12.1m) in annual interest payments on its debt.

Moody's cut Ericsson's long-term debt rating further into high-yield territory from Ba2 to B1 on Monday, and maintained a negative outlook on the rating. The downgrade puts Ericsson level with Alcatel, its French rival. Both companies have seen their credit ratings slip on the back of a prolonged downturn in the telecoms sector. This is the second time Ericsson has been downgraded since its €3bn-rights issue last summer.