Merge Statement is not Working in Sql Server 2012

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SQL-Server-2012

I am using following query for updating records in a table with other table.

MERGE Tarantulla_Whole_dump_BTS_testing AS T

	USING (

		SELECT AnchorShareRequestRef,effective_btstype,Org_effective_btstype FROM Temp_FinalBTS_till_March2012_testing

		) AS S

		ON ( T.AnchorShareRequestRef = S.AnchorShareRequestRef )				

	WHEN MATCHED
		THEN
			UPDATE
			 SET T.effective_btstype = S.effective_btstype, 
          T.effective_btstype_CSV = S.Org_effective_btstype;

But its showing error when i execute it.

Msg 156, Level 15, State 1, Line 2
Incorrect syntax near the keyword 'AS'.
Msg 156, Level 15, State 1, Line 8
Incorrect syntax near the keyword 'AS'.

I only want to update records not insert or delete using merge.