Government forces stormed the town of Maarat al-Numan with a three-pronged attack, entering from the south, west, and eastern sides and backed by intense Russian airstrikes, SOHR said.
Maarat al-Numan is the second largest town in Idlib province which has been in rebel hands since 2012.
Thousands of people were forced to flee to safety further north while others headed toward temporary camps set up near the Turkish border as fighting broke out between rebels and government forces in Maarat al-Numan.
SOHR said regime forces have gained control over 24 villages and towns in Syria in less than four days.
“Authorities, in cooperation with army units, provided all logistic requirements at the corridors, including buses, ambulances, medicines, food supplies, and medical teams to present emergency health services to the people,” the pro-government outlet added.
The latest renewed fighting in the nearly nine-year-long civil war comes just a week after Turkey, which backs the government in Tripoli, and the United Arab Emirates, Egypt, and Russia agreed with Western powers to push for a lasting cease-fire and uphold an arms embargo.
“The United States is monitoring with grave concern the situation in northwest Syria where the combined forces of Russia, the Iranian regime, Hezbollah, and the Assad regime reportedly are conducting a large-scale assault upon the people of Idlib and western Aleppo provinces,” Pompeo said.
“These forces reportedly are conducting indiscriminate aerial bombardment and ground attacks that have trapped thousands of civilians under bombardment in Maarat al-Numan, leaving them nowhere to flee.”
Pompeo added that the United States is “prepared to take the strongest diplomatic and economic actions against the Assad regime and any state or individual that aids its brutal agenda.”
In September 2018, Turkey and Russia agreed to turn Idlib into a deescalation zone, prohibiting acts of aggression.