(Adds comments, background, detail)
WASHINGTON, Feb 5 (Reuters) - The United States is "very very worried" about the escalation in Syria's northwestern province of Idlib, led by an assault by Syrian government forces and supported by Russians, and was also seeing active support of Iranian militia and Hezbollah on the ground, the top U.S. envoy for Syria said on Wednesday.
"This is a dangerous conflict. It needs to be brought to an end. Russia needs to change its policies," James Jeffrey, U.S. Special Representative for Syria Engagement and fight against Islamic State told reporters in a briefing.
The Idlib violence has accelerated in recent months despite several ceasefire efforts, including as recently as January.
On Wednesday, Syrian government forces entered Saraqeb in Idlib, a war monitor and eye witnesses said, in a renewed push by President Bashar al-Assad to recapture the last rebel stronghold.
"We're seeing not just the Russians but Iranians and Hezbollah actively involved in supporting the Syrian offensive. We don't know whether the offensive is just to get to the M4-M5 road, or it may continue further," Jeffrey said, in reference to the strategic highways connecting Syria's Aleppo to Hama and Latakia on the Mediterranean coast.
Jeffrey also said there have been more incidents of Russia violating the terms of the mutual de-confliction agreement in northeastern Syria, in what appeared to be an attempt to challenge the U.S. presence in the region.
(Reporting by Humeyra Pamuk; Editing by Chris Reese and Andrea Ricci)
Our Standards: The Thomson Reuters Trust Principles.