U.S. President Donald Trump spoke by phone with Turkish President Recep Tayyip Erdogan on February 16, "expressing concern over the violence in Idlib, Syria," according to White House press secretary Judd Deere.
Trump called for Russia to end its support for the Syrian regime's "atrocities" and conveyed the United States' "desire to see an end to Russia's support" for Syrian President Bashar al-Assad.
He urged "a political resolution to the Syrian conflict," which has lasted for nearly nine years.
Their conversation came a day before a new round of talks are scheduled between Ankara and Moscow who back opposing sides in the conflict.
Backed by Russian air strikes, Syrian government forces made significant advances on February 16 in the country's Aleppo province, seizing most of the last rebel-held region.
Turkey, which supports rebels who want to remove Assad from power, has urged Russia to stop the attacks in the Idlib region, warning it would use military might to drive away Syrian forces unless they withdraw by the end of the month.
By the end of February 16, regime forces "were in control of all the villages and small towns around Aleppo for the first time since 2012," the Syrian Observatory for Human Rights said.
The UN says that, since December, 800,000 people have been displaced due to fighting in the area.