WASHINGTON (Reuters) - Turkey’s head of intelligence has traveled to Washington to meet with U.S. lawmakers and intelligence officials, sources said, in an apparent bid to improve ties with the Americans after a breakdown in the NATO allies’ relationship last summer.

Hakan Fidan, a close confidant of Turkey’s President Tayyip Erdogan, has met with senators to discuss NATO issues and was expected to meet with U.S. intelligence officials later on Friday, according to five sources familiar with the matter, who spoke to Reuters on condition of anonymity.

The killing of Saudi journalist Jamal Khashoggi in the Saudi consulate in Istanbul was discussed in the meeting with members and staff of the NATO Observer Group, a bipartisan group of senators that advocates for the alliance, two sources familiar with the matter said.

But it was not a central subject in discussions with senators and the Turkish side has refrained from making it the focus of their meetings, the sources added.

Top U.S. senators have said they want to punish Saudi Arabia for the killing, despite President Donald Trump’s decision to stand by the long-time ally.

While the two countries have collaborated on the Khashoggi investigation, U.S.-Turkey ties have been strained by disagreements over a number of issues from Syria to Turkey’s desire to buy Russian defense systems.

Relations between Ankara and Washington began to improve after U.S. pastor Andrew Brunson, who was on trial over terrorism-related charges in Turkey, was released in October.

But the NATO allies remain divided on other issues, including U.S. policy in Syria, Ankara’s ambition to purchase Russian missile defense systems and Turkey’s request for the United States to extradite Fethullah Gulen, a cleric Ankara blames for organizing an abortive 2016 putsch. Gulen denies involvement.

Fidan was expected to discuss the murder of Khashoggi, a Washington post columnist and critic of the Saudi Arabia’s Crown Prince Mohammed bin Salman, in his meeting with U.S. intelligence officials, sources said. It was not immediately clear if Fidan was to meet with Gina Haspel, director of the CIA.

The CIA has assessed with medium to high confidence that the crown price, the kingdom’s de facto ruler, ordered the killing of Khashoggi when he visited the consulate on Oct. 2. Saudi Arabia has said the prince had no prior knowledge.

Trump cast doubt on the CIA assessment, saying the agency had not formed a definitive conclusion. U.S. Secretary of State Mike Pompeo has said there was no direct evidence linking the prince to the killing.