Assembly compilation failed using NASM on Windows 7 x64

Question

I tried to compile the following code (test.asm):

section .text       
 global _WinMain@64       

_WinMain@64:       
    jmp _Begin

_End:
    mov esi, 0x77162c51    ;Address of 'WinExec' function
    call esi               ;Error(9)
    ret

_Begin:    
    xor eax, eax
    push eax               ;Error(14)
    call _End
    db "C:\WINDOWS\system32\calc.exe", 0

Here's the command I used :

nasm -f win64 test.asm -o test.o

And here's the following errors I have in output :

test.asm:9: error: instruction not supported in 64-bit mode
test.asm:14: error: instruction not supported in 64-bit mode

I used to code ASM program using MASM32 on the same architecture without any problem. I don't understand this error.

Thanks a lot in advance for your help.