The linoleum staircase that leads up to a nondescript gray door in a building somewhere in Central Berlin is worn and somewhat grimy. Inside, several middle-aged men are clustered around a table littered with newspapers and overflowing ashtrays.

As they sip their glasses of strong black tea, a Kurdish newscast blares out the latest from the frontline in northern Iraq into the smoke-filled room. Men and women in military fatigues march across the screen to a backdrop of rousing martial music, which almost drowns out the men's heated debate.

From behind a slightly greasy counter, an elderly man is selling tea for 50 cents a glass. He gestures to a bowl piled high with white sugar cubes: "You might need one or two." He grins. The man is sporting a faded beige jacket and a white T-shirt with a picture of Abdullah Ocalan, the imprisoned leader of the PKK, the left-leaning Kurdistan Workers Party.

The PKK was banned in Germany in 1993, following a series of attacks on Turkish institutions and travel agencies. In Berlin, displaying the PKK's green, yellow and red flag or pictures of Ocalan can result in criminal proceedings. So, does the man button up his jacket when he leaves the small flat, I ask, turning to my guide, Ali, a man in this mid-50s with a neat moustache. He shrugs, then shakes his head. "No, we're not afraid." And, he adds, police often turn a blind eye.

'Fighting a just cause'

Ali leads the way to a small courtyard overshadowed by drab office blocks, and points to a rickety plastic chair and a small table. He is, as he puts it, "in charge of public relations for this place."

Ali gestures vaguely to the men in front of the TV and two young women smoking in a corner of the courtyard. The place, he says, is a Kurdish club, where people come to mingle and chat - and whose members, he says, all support the PKK. Not all of them are Kurdish: some are attracted by the organization's militant left-wing ideology.

Given the chance, Ali launches into a long-winded praise of the PKK: its embrace of equality, its democratic credentials, its anti-capitalism. When stopped mid-flow with a question he deems irrelevant, he leans back on his rickety chair, frowning. One such question is why he supports the PKK in the first place. He brushes the question aside: It's a no-brainer, he says: "They're fighting for a just cause."

Ali's heavily-accented German speaks of a childhood in a small town in eastern Turkey. He fled to Germany in 1972 after a particularly brutal beating by the local police when, at 13, he once again had chatted in Kurdish with his fellow pupils.

"They threatened to kill me the next time they saw me, so I left," he says. It was the early 1970s, when, in its attempt to fully assimilate its Kurdish population, the Turkish state resorted to repressive, sometimes violent measures - and speaking Kurdish, listening to Kurdish music, even giving a child a Kurdish name could result in long prison sentences.

Deep roots in Germany

In response, the PKK launched a guerrilla war against the Turkish state in the early 1980s. Many of his friends in Turkey joined the fight, Ali says. Had he stayed in Turkey, he would probably be dead by now: "Many of my friends just disappeared."

Instead, Ali did what he could to support the cause from Germany. He organized and marched at rallies, and invited speakers for public events organized by the PKK's political branch in Europe.

But collecting funds for the PKK's military operations - a criminal offence given the PKK's terrorist label - was never part of his job description, he is quick to point out."If someone wants to give money to Kurdish organizations based abroad, well, they're more than welcome to do so." Donations are voluntary, he adds, refuting reports of coercion and blackmail.

According to the German intelligence agency, Germany, which is home to Europe's largest Kurdish diaspora, is an important source of funding for the PKK's military operations. A recent report estimated that some 13,000 out of Germany's 800,000 Kurds constitute the PKK's "core support base."

The real number is probably much higher, according to Gülistan Gürbey, a political scientist based in Berlin. "The PKK is deeply rooted in the Kurdish diaspora," she says.

Time to rethink ban?

Gürbey is convinced that it's time to rethink the PKK's terrorist label in Germany and Europe. "For years, the PKK hasn't resorted violence in Europe," she says, pointing to the PKK's role in fighting against the advance of the Sunni-extremist militia "Islamic State" (or ISIS/ISIL, as it is sometimes referred to) in northern Iraq and Syria.

"The PKK is fighting against an existentialist threat in the region," she says, adding that this may explain the more positive image it has received in recent months.

Gürbey is referring to comments by several German politicians, including the PKK's long-term supporters in the left-wing party, Die Linke, who share their anti-capitalist outlook and have called for a revaluation of the ban. But others have also weighed into the debate. Social Democrat Rolf Mützenich tells DW that "now is a good moment to recall the developments in Turkey."

In late 2012, the Turkish state and the PKK launched a peace process that has resulted in a ceasefire and ongoing talks. Should the two sides really reach a lasting agreement, Mützenich says, it would be time for a political debate on the PKK's status in Germany and Europe. But, he adds, it might take years until an agreement is reached.

But Mützenich is quick to stress that any rethinking of the ban has to be regardless of PKK's fight against the "Islamic State." And, he adds, his view is that of a foreign policy expert. "Others, including in the Interior Ministry, may be more skeptical."

Colleagues in parliament, such as Volker Kauder from Chancellor Angela Merkel's CDU, are quick to dismiss the entire debate. "No, the question of the PKK's status is not something we're thinking about changing," he tells DW. It's a stance shared by the Interior Ministry. A speaker stressed that while the PKK has refrained from violent acts in Europe in recent years, it's relations to violence remains "tactical."

Growing support for the PKK?

Violence? Zübeyir Aydar, the leading member of the PKK's political branch in Europe, the KCK, dismisses the accusation. "We adhere to German laws," Aydar tells DW on the phone from Brussels, where many leading members are based.

He's following the German debate closely, he says, stressing that it's long-overdue. He does, however, concede that the PKK might revert to violence in Turkey should the peace process break down. "That would lead to a difficult situation, which might lead to a renewed outbreak of fighting. But that's not what we want, we prefer a political solution," he says.

Back in the Kurdish club in Berlin, Ali is frowning again. He's mulling the question of what he would do should any of his three children decide to join the PKK's fight against the "Islamic State."

After a while, he shrugs: "I'd neither tell them to go or stay, it's their own decision." Then he leans across the table: "There are a lot of things I would do, if I was still strong." Abruptly, he stands and leaves - only to return with two more glasses of black tea.