The United States, Germany, France and the United Kingdom have all called for de-escalation in Syria, where rebels have marched on government-controlled areas in the past few days, reigniting violence in the 13-year-long conflict.

An alliance of Syrian rebel factions led by the Islamist Hayat Tahrir al-Sham (HTS) reportedly seized control of Aleppo over the weekend. Syrian President Bashar Assad announced a counteroffensive, launching airstrikes with the help of allies.

Syrian and Russian airstrikes on the rebel-held city of Idlib in northwestern Syria killed at least 25 people, the opposition-run rescue service White Helmets, said early on Monday.

Assad's army also said it had recaptured several towns from the rebels.

What did the NATO countries say?

In a joint statement late on Sunday, the US, the UK, France and Germany urged the protection of civilians and infrastructure "to prevent further displacement and disruption of humanitarian access."

"The current escalation only underscores the urgent need for a Syrian-led political solution to the conflict," in line with UN Security Council Resolution 2254, the statement added.

The 2015 resolution calls for peace talks between the Syrian government and opposition forces.

The rebels began their offensive against the Syrian government on November 27 and have been moving southward into Hama Province after the attack on Aleppo.

rmt/wd (AFP, dpa, Reuters)