Clashes, shelling and air raids in western Syria tainted a Russian brokered ceasefire that aims to end nearly six years of war and lead to peace talks between rebels and the ruling regime.

Syrian regime warplanes carried out nearly 20 raids against rebels in several towns along the provincial boundary between Idlib and Hama, the Syrian Observatory for Human Rights said.

Clashes between rebel groups and regime forces took place overnight in the area, the Observatory and rebel officials said.

Russian President Vladimir Putin, a key ally of Syrian regime head Bashar al-Assad, announced the ceasefire on Thursday after forging the agreement with Turkey, a longtime backer of the opposition.

The truce went into force at midnight but monitors and rebels reported almost immediate clashes, and violence appeared to escalate later on Friday as warplanes bombed areas in the country’s northwest, they said.

Asaad Hanna, a political officer in the Free Syrian Army (FSA), a loose alliance of insurgent groups, told Reuters violence had reduced but had not stopped.

“We cannot be optimistic about someone like the Russians who used to kill us for six years … they are not angels. But we are happy because we are reducing the violence and working to find a solution for the current situation,” said Hanna.

The ceasefire is meant as a first step towards fresh peace talks, after several failed international efforts this year to halt the conflict, which began as a peaceful uprising and descended into war in 2011.

Moscow is keen to push ahead with peace talks, hosted by its ally Kazakhstan. But the first challenge will be maintaining the truce, which looked shaky on Friday.