LONDON (Reuters) - Britain on Wednesday said Ukraine's air defences were having success against Russian jets, likely preventing Russia from controlling the airspace.

       "Ukrainian air defences appear to have enjoyed considerable success against Russia's modern combat aircraft, probably preventing them achieving any degree of control of the air," the Ministry of Defence intelligence update posted on Twitter said.

       Britain's assessment also said Russian forces had failed to make any significant breakthroughs in fighting north west of Kyiv.

       (Reporting by William James; Editing by Shri Navaratnam)