Turkish President Recep Tayyip Erdogan has accused the U.S. national-security adviser of making "a very serious mistake" by demanding that Turkey not harm Kurdish fighters in Syria as President Donald Trump plans to withdraw U.S. troops from the war-torn country.

"John Bolton has made a very serious mistake. We cannot make any concessions in this regard," Erdogan said on January 8, just before Bolton left Turkey with tensions between Washington and Ankara at new highs.

Bolton visited Ankara to seek assurances that Turkey won't attack U.S.-allied Kurdish militia in northeastern Syria that Ankara views as terrorists.

He held a two-hour meeting at the presidential complex in Ankara on the morning of January 8 with Ibrahim Kalin, a senior adviser to Erdogan.

A spokesman for the U.S. National Security Council, Garrett Marquis, said in a statement the two sides had identified further issues for dialogue and that the United States looks forward to ongoing military-to-military consultations.

But in what was reported in Turkey as a "snub" over disagreements about Kurdish fighters in Syria, an expected meeting between Bolton and Erdogan did not take place on January 8.

Marquis said U.S. officials were told Erdogan would not meet with Bolton because of local election campaigns in Turkey and because of a speech that the Turkish president was due to give to parliament.

Erdogan later told reporters there was no need for him to meet Bolton.

Just hours after Bolton's visit to the presidential complex in Ankara, Erdogan said in his speech that Turkey's preparations for a new military offensive against terrorist groups in Syria are "to a large extent" complete.

He criticized Bolton over comments suggesting the United States would prevent attacks on Syrian Kurdish fighters.

Erdogan said that "those involved in a terror corridor" in Syria "will receive the necessary punishment."

There also was no immediate word on whether Bolton held an expected meeting with Turkish Defense Minister Hulusi Akar and intelligence chief Hakan Fidan.

Bolton said before his visit he would seek assurances that Turkey won't attack Kurdish militia fighters in Syria who are allied with the United States in the fight against Islamic State extremists.

Bolton said that is a "condition" for Trump's planned withdrawal of American forces in northeastern Syria.

Bolton's visit to Ankara parallels a similar trip to the region by Secretary of State Mike Pompeo and follows Trump's abrupt announcement that he was ordering 2,000 U.S. troops out of northeastern Syria.

Trump's announcement stunned U.S. allies and led to the resignation of U.S. Defense Secretary Jim Mattis.

U.S. officials and others fear that a U.S. pullout could destabilize Syria further and lead to the slaughter of Kurdish militias who have been fighting alongside U.S. forces.

Prior to visiting Turkey, Bolton traveled to Israel, which has also been concerned about a U.S. withdrawal.

In Jerusalem, Bolton walked back Trump's initial announcement, saying instead that the United States wanted to ensure that Islamic State "is defeated and is not able to revive itself and become a threat again."

But he also said Turkey must agree to protect the U.S. Kurdish allies.

In an opinion piece published by The New York Times on January 7, Erdogan warned that the U.S. withdrawal must be planned carefully and carried out with the right partners.

Erdogan said Turkey was the only country "with the power and commitment to perform that task." He also wrote that Turkey was committed to defeating Islamic State and "other terrorist groups" in Syria.

In comments broadcast on January 7 on CNBC, Pompeo said that Erdogan had promised to protect Kurdish fighters in Syria.

Pompeo this week is visiting eight Arab capitals to discuss Syria, as well as discuss U.S. efforts to contain regional power Iran.

The U.S.-backed Syrian Kurdish People's Protection Units form the backbone of the opposition Syrian Democratic Forces.

But Turkish authorities say those Syrian Kurdish fighters are linked with the Kurdish Workers Party (PKK), which is banned in Turkey and has been considered a terrorist group by the United States since 1997.

With reporting by Reuters, AP, AFP, and The New York Times