BEIRUT, Lebanon — The Turkish government took the extraordinary step on Wednesday of asking the United States to stop Kurdish commanders from diverting their forces from areas of eastern Syria to the fight in Afrin in the west.
The request followed an announcement from the Kurdish forces, which are allied with the United States in the fight against the Islamic State militant group, that they intended to send 1,700 fighters from Deir al-Zour, a strategically important eastern province, to the fight against Turkey in Afrin, a Kurdish enclave.
Ibrahim Kalin, a spokesman for President Recep Tayyip Erdogan of Turkey, said his country had taken “the necessary steps” through official channels and “expected from the U.S. that it should absolutely step in” to prevent the movement of the Kurdish forces from Manbij to Afrin. “This is our most natural right,” Mr. Kalin added.
It was not clear why Mr. Kalin had referred to Manbij, a city at the westernmost point of the Syrian territory held by the Kurds, though it might have been cited as a way station for the troops as they moved toward Afrin.
There was no immediate American response to the request by the Turks, an American ally and NATO member that invaded Afrin in January and threatened to drive the Kurds from the entire Syria-Turkey border. But the Turkish assault has since bogged down.
The fighting in Afrin is creating problems for the United States. The transfer of personnel from the Kurdish-led, American-backed militia known as the Syrian Democratic Forces, or S.D.F., is a blow to Washington’s effort to stamp out the last vestiges of the Islamic State, also known as ISIS.
On the diplomatic front, the Americans have insisted that although they are allied with the S.D.F. in eastern Syria, they have no affiliation with the group in the northwest and will not aid any of its operations there. But with its Kurdish coalition allies now streaming to join the defenders in Afrin, that posture will be increasingly difficult to maintain. As a result, in Afrin, the Trump administration is finding itself awkwardly on the opposite side from Turkey.
The S.D.F. said in a statement on Tuesday that it had made a “painful decision” to move the fighters from Deir al-Zour to Afrin, citing “the failure of the international community” to pressure Turkey and “stop its madness within our Syrian borders.”
The role in Afrin of the Kurdish militia known as the People’s Protection Units, or Y.P.G., which is the main component of the S.D.F., has raised tensions with Turkey, which considers the militia an extension of a separatist group that is active in Turkey and is listed as a terrorist group by both Ankara and Washington.
For six weeks, Turkey has mounted a campaign to wrest control of Afrin from the Y.P.G., an offensive that has displaced some 10,000 people and killed several hundred civilians and 41 Turkish soldiers. Mr. Erdogan said this week that 159 Syrians belonging to the Free Syrian Army, which is fighting alongside Turkish armed forces, had also died.
The Y.P.G. has responded with cross-border shelling, leading to civilian deaths in Turkey.
Adding to the complications, the Y.P.G., which has carved out a zone of de facto autonomy from the Syrian government within Afrin and in a larger swath of northeastern Syria, last week allowed some pro-government militias to enter its territory to help the fight against Turkey.
The militias did not include formal army troops, but they flew the Syrian government flag. State television in Syria said the militias were aiding in the defense of the country’s borders but made no reference to Kurdish aspirations.
Turkey’s incursion came soon after the United States said that it would continue to support the S.D.F. even after the fight against the Islamic State ends and that it would help the group form a border force to protect the long frontier its territory shares with Turkey.
Now, the movement of troops away from Deir al-Zour threatens two American objectives there: preventing a resurgence of the Islamic State and curbing the growing influence of Iran, which sponsors militias that fight for the Syrian government.
In another crisis point in Syria, negotiations on Tuesday between the government and Jaish al-Islam, the rebel group that controls the northern and eastern parts of the Damascus suburb of eastern Ghouta, went nowhere. Despite mass civilian casualties and major territorial losses, the armed groups in the enclave refused to withdraw, according to antigovernment activists.
“The result of the negotiations which Jaish al-Islam took part in yesterday is that the displacement and exit of the armed groups and civilians was refused completely,” said Alaa al-Ahmad, an activist in eastern Ghouta, adding that rebel groups had “refused a policy of displacement.”
Videos published by Syrian pro-government news media showed some residents of the town of Hammouriyeh taking to the streets Wednesday afternoon calling on the rebel fighters to leave. The videos, in which some people could be seen waving Syrian government flags, could not be independently verified.
The residents of eastern Ghouta have lived under a harsh government siege since 2013 and have borne the brunt of a heavy bombing campaign that has pounded the enclave for weeks, claiming the lives of over 800 civilians to date. The bombardment has continued despite a unanimously approved 30-day cease-fire agreed to by the United Nations Security Council that was intended to provide respite and an opportunity for civilians to evacuate.
After the failed negotiations, about 700 fresh pro-government troops arrived on Wednesday, the Syrian Observatory for Human Rights reported, in preparation for a push into the urban heart of the rebel-held enclave.
Syrian and Russian authorities maintain that rebels have shelled the humanitarian corridor and prevented civilians from leaving. The Russian Ministry of Defense, in a briefing on Wednesday, maintained that only 17 people had thus far been able to evacuate through the corridor.
Since the onslaught began less than a month ago, pro-government forces have seized about 40 percent of eastern Ghouta, mostly rural areas. Government forces have exploited loopholes in the cease-fire agreement to continue their advance.