"There have been disagreements within the organisation and we apologise to honest members who broke from our ranks," senior cadre Duran Kalkan told Europe-based Roj TV late on Sunday.
"I call on the disgruntled and the offended to come back," he added in a rare act of PKK self-criticism.
His appeal came after he and about 40 fighters - including Osman Ocalan, the estranged brother of PKK founder Abd Allah Ocalan, who is serving a life sentence in a Turkish jail - broke off from the armed group and set up their own party.
But Kalkan appeared to exclude from his appeal Osman Ocalan, a long-time confidante of his brother and once a senior PKK commander who dropped out last summer and formed the Patriotic Democratic Party in Mosul, northern Iraq, according to Turkish press reports.
"This needs to be taken seriously. Actions such as this, which
harm unity, are definitely dangerous," Kalkan said. "Our attitude toward traitors is very clear."
Ocalan's departure was a further blow to the PKK, now called KONGRA-GEL, which was already weakened by factionalism.
Should Ocalan and his breakaway group threaten the PKK, Kalkan warned, they would be the "losers".
The PKK wants self-rule in the
east and southeast of Turkey
The PKK took up arms against Turkey in 1984 for self-rule in the predominantly Kurdish east and southeast of the country in a 15-year conflict that has claimed about 37,000 lives.
After Abd Allah Ocalan was captured in Kenya, brought back to stand trial in Turkey and sentenced to life in prison for treason in 1999, the PKK announced a unilateral ceasefire and withdrew from Turkey into neighbouring northern Iraq in an attempt to seek a peaceful resolution to the dispute.
But the group, pressed by the United States to leave the area and finding little support from other Iraqi Kurdish leaders, ended the five-year-old truce on 1 June, threatening to start attacks across Turkey.