Scott Weiland FIRED -- Stone Temple Pilots Fire Lead Singer

Stone Temple Pilots has unceremoniously FIRED its lead singer Scott Weiland ... who's been the face of the seminal rock band for more than 20 years.

The group released an ominously curt statement today, saying, "Stone Temple Pilots have announced they have officially terminated Scott Weiland." They don't give any further explanation.

It's pretty shocking for several reasons ... the main being Weiland has been a core member of the group since it came together in 1986. His voice has become synonymous with STP's sound ... on hits like "Plush," "Sour Girl," and "Sex Type Thing."

Another reason this came out of nowhere ... Weiland denied rumors he was leaving the band just yesterday, telling Rolling Stone, "STP has not broken up. I haven't quit. I haven't been fired."

Rumors of a split began a couple of months ago when Slash said STP had fired Weiland.

STP reformed in 2008 after a 5-year hiatus and toured through last year -- but apparently it hasn't been working out.

So far, it's unclear who STP has in mind to replace Weiland ... if anyone.

Weiland is set to launch a solo tour next month.