CAIRO (Reuters) - Egyptian security forces have killed 12 armed militants in the country's western desert, in an operation carried out after a deadly attack on a police convoy last week, MENA state news agency said on Friday.

"Security forces dealt a severe blow to the terrorist elements in revenge for the blood of the men who were martyred last week in the oasis," MENA said citing a high-level security source. "Twelve terrorist elements were killed this morning in violent clashes."

Authorities say the attack last week hit a police operation in a remote area in Giza governorate, 135 km outside Cairo. Friday's operation was in New Valley governorate, further south, which shares a long border with Libya.

MENA did not say to which group the militants belonged. Egyptian forces have been battling several insurgencies, mostly focussed on an Islamic State affiliate that has killed hundreds of police and troops in the northern Sinai since 2013.

(Reporting by Omar Fahmy; Writing by Patrick Markey; Editing by Robin Pomeroy and Jon Boyle)