Istanbul -- President Barack Obama and Turkey's Prime Minister Recep Tayyip Erdogan had a daunting agenda when they met at the White House last week. The Syria crisis was top of the list. The peace process between Turkey and the PKK was also a priority. The United States can help address both problems by removing the PKK from its list of Foreign Terrorist Organizations (FTOs). Sequencing is important. Delisting the PKK should occur at a time when it has maximum impact on events in Syria, as well as Turkey's domestic peace process.

The situation in Syria is urgent. Delisting the PKK would open the door to discussions with the Democratic Union Party (PYD), the PKK's affiliate in Syria, about joining the opposition to Syria's President Bashar al-Assad. It would also boost the peace process in Turkey by rewarding the PKK for its recent decision to cease hostilities and withdraw fighters from Turkish soil, maintaining momentum and setting the stage for negotiations aimed at a full final solution to Turkey's Kurdish question. Waiting would leverage the PKK's continued cooperation, but risks diminishing the impact of delisting on regional events.

The PKK conflict is rooted in history. Kurds are the largest stateless minority in the world, with an estimated 30 million in Turkey, Iraq, Iran and Syria. More than half live in Turkey, where they represent 20 percent of the population. Though the 1920 Sevres Treaty promised Kurds a state of their own, it was replaced with the 1923 Treaty of Lausanne, which denied the national aspirations of Kurds. The 1925 and 1937 insurgencies were brutally suppressed. Turkey denied the very existence of Kurdish culture and language, banning geographical place names in Kurdish and calling Kurds "Mountain Turks." After the 1980 military coup, the junta adopted a draconian constitution banning all demonstrations of Kurdish identity. It also established martial law in the Kurdish regions of Southeast Turkey, pursuing a scorched earth policy that displaced millions of Kurds.

Abdullah Ocalan founded the Kurdistan Workers Party (PKK) in 1974 as a Maoist proletarian movement. The PKK's charter "condemned the repressive exploitation of the Kurds" and called for "a democratic and united Kurdistan." Kurds in Turkey revere Ocalan for fighting the military and demanding social justice.

Correspondingly, Ocalan is reviled by many Turks who hold him responsible for the deaths of more than 30,000 civilians that spanned three decades. The PKK initially targeted Kurds working for state institutions, as well as pro-government militias. By the mid-1990s, however, the PKK shifted tactics, focusing its military operations on the security services and regime symbols. It also abandoned its goal of a Kurdish homeland, seeking instead greater political and cultural rights in Turkey.

At Turkey's urging, the United States listed the PKK as an FTO in 1997. The European Union added the PKK to its list of terror organizations in May 2002. NATO and more than 20 countries also classified the PKK as a terror group. FTO designation stigmatizes and isolates designated terrorist organizations. It also carries travel bans and financial restrictions. The 2011 Anti-Terrorism Act makes it a criminal offense to provide material resources or counsel to terrorist organizations and prohibits their representatives from entry to the United States.

Arduous procedures are required for an organization to get off the FTO list. Under the Intelligence Reform and Terrorism Prevention Act of 2004, the FTO may file a petition for revocation two years after its designation. It must provide evidence that the circumstances are sufficiently different to warrant revocation. The Secretary of State may delist at any time if the circumstances have sufficiently changed, or if the national security of the United States warrants revocation.

Delisting is essentially a political decision. Technical reasons for listing the PKK as an FTO have changed. So has the political context, given the current peace process and the crisis in Syria. In consultation with Turkey, the Obama administration should consider when delisting of the PKK would have maximum impact. I recently asked a senior Turkish official about delisting (who was not authorized to speak on the record). He replied, "Why not?"

A strong case can be made for delisting sooner than later. Ocalan was arrested in 1999 and sentenced to life in prison. From his cell on Imrali lsland, Ocalan has become an advocate for peace and reconciliation among Turkish citizens, including those of Kurdish origin. Proclaiming the recent peace initiative on March 21, 2013, Ocalan wrote: "We reached the point where weapons should go silent and ideas speak."

Turkey is at a historic crossroads. Erdogan has promised greater political and cultural rights to Kurds. In return, Ocalan endorsed a cease-fire and withdrawal of PKK fighters from Turkey after lengthy negotiations. The deal was hammered out during negotiations between Ocalan and Erdogan's special envoy, Hakan Fidan, who heads Turkey's National Intelligence Agency. Public opinion polls indicate that 70 percent of Turks support the peace process. There has been no PKK-related violence for more than 4 months.

The United States has delisted FTOs before to incentivize peace. Other groups removed from the list during a peace process include the Irish Republican Army (IRA) and the Palestinian Liberation Organization (PLO). Groups have also been delisted when circumstances change. Even the Mujahedin Khalq, which was responsible for hostage-taking at the U.S. Embassy in Tehran, was recently delisted.

Attitudes in Europe are also evolving. In April of 2008, the Luxembourg-based Court of First Instance said that decisions made by EU governments in 2002 and 2004 to list the PKK as a terror group and freeze its assets were illegal under EU law. On April 24, the Parliamentary Assembly of the Council of Europe changed its terminology for describing PKK militants to "activists." The European Parliament is also debating a resolution to remove the PKK from the EU's terror list.

The Syria crisis is a big factor in Erdogan's approach. Last week's attack in the Turkish town of Reyhanli, which killed more than 50 Turks, underscores the potential spillover of conflict from Syria. Erdogan wants the U.S. to use its military capacity for regime change in Syria. But this will not happen until the Syrian opposition coalesces around a plan for governing Syria after Assad.

The Syrian National Council, the leading opposition group, must involve Syria's minorities -- Kurds, Allawites, Druze, and Christians. Kurds represent 15 percent of the population. However, factionalism limits inter-Kurdish cooperation, Kurdish engagement with other minorities, and the broader opposition.

Engaging the PYD would be a big step towards forging consensus. Neither the United States nor the EU will act without Turkey's blessing. To this end, a deal could be made for the U.S. and EU to delist the PKK. In exchange, Ocalan would instruct the PYD to work with the opposition. The PYD has an effective fighting force on Turkey's border near Qamishli in the North and East of Syria. Engaging the PYD would establish a buffer between the war in Syria and Turkey, enhancing Turkey's security, and fostering a common vision for governance and regional cooperation when Assad is deposed.

Mr. Phillips is Director of the Program on Peace-building and Rights at the Institute for the Study of Human Rights.