Where can I download asm(assembler) not c compiler for writing apps for I phone 6

I am interested in writing some cell phone apps in ARM assembly language. I would like to write them for Apple I phone 6  and Android Samsung S5. I am very familiar with writing in Assembly language on the IBM main frame and X86 personal computers. What learning materials are available from ARM to help me learn ARM assembly language. I also need to know the software and hardware required to assemble the apps.