A man was found fatally stabbed this afternoon outside of the Castro post office, and officials say that he had a knife sticking out of his chest. According to the Chronicle, police arrived on the scene just before 3:00 p.m., and as of this time are unsure whether the wound was self-inflicted or the work of an assailant.

The man was pronounced dead at the scene, and Hoodline reports that the area around 18th and Diamond Streets was roped off with police tape.

"My boyfriend saw police units in the area and a body being covered," a tipster named Peter told Hoodline. "A Mollie Stone's worker said it was a stabbing."

The man appeared to be in his 60s, and Muni in the area was delayed while the street was closed.

Update: SFist reader Chantel Beam tells us she witnessed the immediate aftermath. "The guy was just laying on the sidewalk with a kitchen knife sticking out of his chest with blood all over him and was shaking. About a minute later about 20 cops showed up and rushed to him to help. They had us leave as they were taping off the street."

Today's incident is only a few blocks away from the 3900 block of 17th Street where a man was stabbed in the neck this past May. In that case the victim was waiting for Muni, and police arrested the alleged attacker.

Update 2: Hoodline confirms that police are treating the incident as a suicide, and they found a suicide note on the man, who has been identified as 63-year-old Peter Robinson, originally of Madison, Wisconsin.

Related: Man And Woman Dead In Separate San Francisco Slayings Thursday