reduce tablespace

i want to reduce size of below tablespace
Tablespace ID = 101
Name = TS_RPP_DATA_DEC_12
Type = Database managed space
Contents = All permanent data. Large table space.
State = 0x0000
Detailed explanation:
Normal
Total pages = 1444672
Useable pages = 1444656
Used pages = 272
Free pages = 1444384
High water mark (pages) = 624
Page size (bytes) = 16384
Extent size (pages) = 16
Prefetch size (pages) = 192
Number of containers = 1

but when ever i tried to
db2 "alter tablespace TS_RPP_DATA_DEC_12 reduce (all 100m)"
it gives me below error
bash-3.2$ db2 "alter tablespace TS_RPP_DATA_DEC_12 reduce (all 100m)"
DB21034E The command was processed as an SQL statement because it was not a
valid Command Line Processor command. During SQL processing it returned:
SQL20170N There is not enough space in the table space "TS_RPP_DATA_DEC_12"
for the specified action. Reason code = "1". SQLSTATE=57059