Vice President Biden, left, talks as Turkish Prime Minister Ahmet Davutoglu looks on during a joint news conference following their meeting Saturday at Dolmabahce Palace in Istanbul. (Sedat Suna/Associated Press)

Turkey and the United States continued Saturday to disagree about the status of Kurdish forces who have become a key part of the U.S. strategy to defeat the Islamic State in Syria.

In statements after a two-hour meeting here, Vice President Biden and Turkish Prime Minister Ahmet Davutoglu praised the sometimes rocky U.S.-Turkish alliance. Calling Turkey a “strategic partner,” Biden said the relationship is “enduring, it’s rooted in history, it’s in the hearts of our people.”

But in the stew of overlapping conflicts, regional rivalries and competing interests in the civil war in Syria, and the expansion of the Islamic State in Syria and Iraq, U.S.-Turkey ties have often been strained. Biden’s visit here was intended to shore them up, officials traveling with him said, and to add some high-level impetus to resolving a range of issues.

Standing at Biden’s side for statements after their meeting, Davutoglu repeatedly referred to Syrian Kurds allied with the United States — a fighting force called the People’s Protection Units and known as YPG — as a terrorist organization on par with the Islamic State and in league with Turkish Kurds, who have recently escalated a long-standing campaign of secessionist violence in southeastern Turkey.

Despite Davutoglu’s frequent references to the “terrorist” YPG, Biden never mentioned them. He referred only to Turkey’s Kurdistan Workers Party, known as the PKK, which the United States agrees is a terrorist organization.

“We want to make sure, because it’s such an important relationship . . . that there is no misunderstanding” with Turkey, Biden said. “That where we agree, we agree with precision; where we have disagreement, we state it flatly.” On strategic issues, including the need to work together to defeat the Islamic State, he said, “there is no disagreement.”

The Syrian Kurds have become a major sticking point, both in U.S.-Turkey collaboration against the Islamic State and in coming negotiations to end a civil war in Syria that the United States considers a distraction from the larger anti-terrorist fight. The negotiations, between representatives of Syrian President Bashar ­al-Assad’s government and Syrian opposition forces, were scheduled to begin Monday in Geneva but now appear to have been postponed.

Secretary of State John F. Kerry, after meeting in Riyadh with foreign ministers from the six nations in the Gulf Cooperation Council, said he was confident that an initial negotiating session would take place. The warring participants won’t be at the same table or even in the same room, but they will be at the same venue while U.N. Special Envoy Staffan de Mistura acts as a go-between.

“We want to keep the process moving and put to full test the readiness and willingness of people” to achieve peace, Kerry said.

Kerry noted that there are sharp divisions over the future of Assad. The United States insists that Assad must eventually leave power and elections be called within 18 months of a cease-fire and peace talks starting.

“We know that the war in Syria cannot end — it’s not that it will not end, it’s not that people choose otherwise — it’s that it cannot end, because he is the magnet that attracts the violent terrorism and jihadis who will continue to come as long as he or his supporters insist he is a part of a long-term future,” Kerry said.

Part of the reason for the delay is a dispute between Russia and Turkey, which shot down a Russian fighter jet that crossed over its border from inside Syria in November. Russia, which provides military assistance to Assad, has joined the United States in promoting the negotiations. But it insists, in what appears to be an effort to strike back at the Turks, that the YPG be included as part of the opposition delegation. If that happens, Turkey has said it will withdraw its support for the talks.

With the bulk of the Syrian opposition focused on fighting Assad, the United States last year turned to the YPG as a capable fighting force — and the only one available to it with thousands of fighters — to wage war against the Islamic State on the ground. Since early last year, the Syrian Kurds have gradually cleared much of the Syrian side of the lengthy Turkish border, supported by U.S. airstrikes.

Turkey does not want them to move any farther, particularly to the western portion of the frontier, where a 65-mile strip remains under Islamic State control and is used for moving foreign fighters and goods into Syria.

Both the United States and Turkey want to drive the remaining militants from the area but have so far failed to assemble a mutually agreeable, non-Kurdish force to occupy it on the ground. “The challenge is getting enough warm bodies willing to prioritize the fight against [the Islamic State] over the fight against Assad” in western Syria, said a senior Biden official, speaking on the condition of anonymity to discuss the talks with Turkey.

Turkey says it can supply hundreds, if not thousands, of Syrian Arab and other non-Kurdish opposition fighters for the mission, but it has been slow to do so. The administration, wary of the involvement of Islamist groups within the opposition that Turkey supports, has insisted on a list of names it can vet before arming the fighters and coordinating airstrikes with them. Part of Biden’s mission here was to speed that process.

Long accused of hedging its bets with the Islamic State and allowing passage across its border, Turkey has “taken some very important steps to improve” the situation, Biden said. “American and coalition aircraft are operating out of Turkish bases” and have “ramped up the air campaign against ISIL targets to the highest tempo since the beginning” of the airstrikes in the fall of 2014, he said. ISIL is another name for the Islamic State.

Biden also solidified a U.S. offer of border-monitoring assistance, including aerostat balloon-mounted cameras and tunnel-
detection equipment, along with increased intelligence sharing to give the Turks more visibility on the border.

Morello reported from Riyadh, Saudi Arabia.