bowtie2

I’ve downloaded my genome reference index from NCBI ( Human Build 38 patch release 13 (GRCh38.p13).
The downloaded assembly is in fasta.tar format. I ran bowtie2 for mapping and used the command:

 bowtie2-build genome_assemblies_genome_fasta.tar bowtie
the output is:
Warning: Encountered empty reference sequence
Warning: Encountered reference sequence with only gaps
Reference file does not seem to be a FASTA file