"The Turks are assembling forces," McGregor, leading US expert on Middle East war and integrated ground combat tactics in modern warfare, warned.
Lieutenant General Sergei Kuralenko, the commander of the Russian center on reconciliation in Syria, expressed the same concerns about the Turkish buildup to reporters at the Hmeimim airbase near Latakia in Syria on Monday.
Kuralenko confirmed the deployment of reinforcements, including armed vehicles by Turkey on the Syrian border, and he too expressed concern that such moves could lead to the derailment of the fragile three-day-old truce in Syria.
Macgregor agreed that the ceasefire could still be derailed or sabotaged.
"I am not sure this arrangement is more than a temporary respite from the fighting," he said.
Wider conflicts in the region such as Turkey’s continuing feud with its more than 20-million-strong Kurdish minority, or the growing enmity between Sunni and Shia Muslim states and communities in the region, posed long-term, structural threats to the Syrian peace deal, he noted.
"We are at the beginning, not the end of the fighting in the Levant and Mesopotamia," Macgregor cautioned.
Doug Macgregor holds a Ph.D. in international relations from the US Military Academy at West Point and in addition to his practical experience he is also a military historian. He commanded the US armored forces in the Battle of 73 Easting in the 1991 Gulf War, the largest US tank victory since World War II.