WASHINGTON (AP) — The United States and Turkey on Wednesday looked to brush aside differences that have strained relations for years but were unable to report progress in resolving disagreements over Russia's invasion of Ukraine and NATO expansion that have soured ties between the allies.

At a meeting in Washington, Secretary of State Antony Blinken and visiting Turkish Foreign Minister Mevlut Cavusoglu sought to bridge those gaps, but there was no immediate sign that they had, even though both men lauded the partnership between their countries.

They played up cooperation on Ukraine, with Blinken in particular praising Turkey's leadership in securing a deal with Russia for the transport of Ukrainian grain. But in brief remarks before their meeting, neither specifically mentioned their differences over the accession of Finland and Sweden to NATO, which the Turks have so far blocked despite strong support from the U.S. and other allies.

Turkey is demanding that the Swedes do more to rein in Kurdish groups that Ankara sees as a threat to its security before approving the alliance's expansion.

"We are close allies and partners," Blinken said. "That doesn't mean we don't have differences, but when we have differences, precisely because we are allies and partners, we work through them in that spirit."

Cavusoglu made no mention of Finland and Sweden in his comments, but did make a point of stressing the importance Turkey places on winning U.S. approval to buy advanced F-16 fighters, something the Biden administration supports but that faces significant congressional opposition.

Cavusoglu called the F-16 deal a "significant topic" in U.S.-Turkey defense cooperation. "As we have said before, this is not only about Turkey but also for NATO and the United States as well. So we expect approval in line with our joint strategic interest."

Cavusoglu's visit is a rare one to Washington by a top Turkish official as President Joe Biden's administration has kept its distance from Turkey because of President Recep Tayyip Erdogan's increasingly authoritarian direction and policies curbing rights and freedoms.

Positioned at the crossroads between East and West, Turkey remains strategically important for Washington. And, as Blinken pointed out, Turkey was key to the agreement between Russia and Ukraine that allowed millions of tons of Ukrainian grain to be transported to world markets, averting a food crisis during the war.

NATO allies, however, frequently find themselves at odds over a number of issues, with the biggest disputes centering on Turkey's purchase of Russian-made missiles and support for Kurdish militants in Syria.

Turkey's acquisition of the S-400 air defense system from Russia in 2017 led to sanctions and Turkey being removed from the development program for the next-generation F-35 fighter plane. After losing out on the F-35, Ankara is trying to restock its F-16 fleet.

U.S. concern over Ankara's cozy relationship with the Kremlin has been reinvigorated by the war in Ukraine. Despite Turkey's ties with Moscow producing breakthroughs such as the grain deal and prisoner swaps, Washington is worried about sanctions-busting as Turkish-Russian trade levels have risen over the last year.

And, Ankara's feet-dragging over ratifying bids by Sweden and Finland to join NATO has added to friction between the allies.

Turkey's recent attempts at rapprochement with Syria after a decade of bitter enmity have caused another break with the U.S. Following a meeting of Syrian and Turkish defense ministers in Moscow last month, the U.S. State Department reiterated its opposition to countries normalizing relations with Damascus.

The U.S. military has also warned that a threatened Turkish operation against the Kurdish YPG in northern Syria could destabilize the region and revive the Islamic State group.