The PKK said in a statement late on Sunday: "It has been determined that the action in Van on 9 March was undertaken by Devrim Solduk, codenamed Dengtav, on his own initiative and decision."
It also said that the explosion had been an "accident".
"In a letter our friend left, he said he would carry out such an action because the Turkish state launched a destructive process against our leader Apo," it said.
The PKK statement said Solduk was born in 1977 in the southeastern town of Siverek and had studied at Yildiz Technical University in Istanbul before joining the rebels.
Apo is the codename of Abdullah Ocalan, the PKK leader captured by Turkish security forces in 1999 and sentenced to life imprisonment on an island near Istanbul.
Ocalan is reviled in much of Turkey as the man responsible for the death of more than 30,000 people since the PKK launched its armed struggle in 1984 for a Kurdish state in southeast Turkey.
As well as the deaths, 19 people were injured in the 9 March blast, which occurred near the Van governor's office.
Officials said at the time they believed that it was a suicide bomb.