Replace First three character T SQL Query

Hello All,

I have table in which I have a column ITEMID ,ITEMID has data like this 

ITEMID 

ABC001

ABC002

AAA001

Ab0011

Ab0012

AAA02

I have to replace the ItemID which start with AAA and AB to X

ABC001

ABC002

AAA001   -----------X001

Ab0011--------------X0011

Ab0012-------------X0012

AAA02-------------X02

Thanks 

sanjay