"We pushed back very hard at all levels for the Turks not to commence this operation", US Defense Secretary Mark Esper told a news briefing, responding to criticism that Trump had given Turkey a tacit "green light" for its attack.
Turkey kept up its assault on Kurdish-held border towns in northeastern Syria on Saturday on the fourth day of an offensive that is drawing growing global condemnation, even from Washington.
Turkey says its military offensive has taken central Ras al-Ayn, a key border town in northeastern Syria, and its most significant gain since its cross-border operation began against Syrian Kurdish fighters.
The PKK, which seeks an independent Kurdish state in Turkish territory, is considered a terrorist group by Britain and the U.S. as well as Turkey.
Erdogan hopes to create a buffer zone between the border and territory controlled by Syrian Kurdish forces, who have links with Turkey's own Kurdish rebels.
On Friday, the Pentagon said USA troops came under artillery fire from Turkish emplacements though none of its soldiers were wounded near the Syrian border town of Kobani, 60 km (37 miles) west of the main area of conflict.
However, Congress and the Pentagon have stressed the need to protect the Syrian Kurds from Turkey, many pointing out that 11,000 SDF fighters died in the anti-IS campaign.
The Pentagon on October 11 confirmed earlier reports that said an explosion rocked the site near the city of Kobani, illustrating the risk of US and Turkish forces inadvertently coming into conflict in the tense region.
A few hours later, the Pentagon confirmed that United States troops near the northern Syrian border came under artillery fire from Turkish positions.
Navy Captain Brook DeWalt, a Pentagon spokesman, said the artillery explosion came within a few hundred metres of the area where U.S. troops were. The statement said the Turkish border posts were targeted from a Syrian Kurdish position about 0.6 miles southwest of a US observation post. "But the Kurdish people here and the leadership in Turkey should understand that we don't think what President Erdogan did was right".
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What is the U.S. doing?
"The Americans sold us out and we do not expect them to help us fight the Turkish troops", one Kurdish fighter told CNN, as a U.S. flag fluttered over the base.
Aid groups have warned of yet another humanitarian disaster in Syria's eight-year-old war if the offensive is not stopped.
Facing with mounting condemnation, even within his own Republican Party, of his apparent abandonment of a loyal USA ally, President Donald Trump has toughened his policy towards Ankara, threatening it with sanctions if its operation goes too far.
Meanwhile in Congress, lawmakers from both sides of the political divide were preparing legislation to pile pressure on Turkey.
Saturday's meetings in Egypt's capital came as the Turkish offensive against Syrian Kurdish fighters enters its fourth day.
In a statement late Friday, Turkey's Defense Ministry said it did not open fire at the United States facility, and said it struck a Kurdish position after a Turkish position had been attacked with machine guns and mortar fire 1 kilometer (0.6 miles) from a USA observation post.
"We will never stop this step we have taken against the PYD/YPG". Erdogan threatened to send them to Europe if the European Union did not back his assault.
A refugee crisis is developing.
He also plans to use the strip, which he envisions will be about 30 kilometres deep, as an area in which to send back some of the 3.6 million Syrian refugees who live on Turkish soil. Turkish artillery continued to bombard parts of the town, a Reuters reporter said. Thousands of people could lose adequate access to clean water in the Hassakeh region, it reports. "It is that they decided that the immediate benefits of cooperating with the YPG outweighed the longterm concerns of Turkey".