UN aid for civilians entered rebel-held northwest Syria from Turkey via the Bab al-Hawa border crossing, the first such convoy since a Security Council mechanism expired in July.

The convoy "consists of 17 trucks loaded with various relief materials from the United Nations", said Mazen Alloush, a border official on the rebel-held side.

An AFP correspondent saw trucks pass through the crossing bearing signs with the logo of the World Food Programme and the Food and Agriculture Organization.

Under a 2014 deal, aid for millions of residents of Syria's last remaining rebel strongholds in the country's north and northwest had largely passed through the Bab al-Hawa crossing -- without the authorisation of Damascus.

But in July, the Security Council failed to reach consensus on extending the mechanism, and the UN said a subsequent Syrian offer to keep the crossing open for another six months contained "unacceptable" conditions.

Last month, the UN announced it would resume the aid deliveries after reaching an agreement with Damascus for a six-month period, in a deal that raised concerns among relief groups who wanted Syrian authorities kept out of the process.

The UN humanitarian agency OCHA said Tuesday's convoy delivered "50 tons of assistance".

It included "hygiene kits and educational items for some 46,000 people, nutrition support for 10,000 babies, tents and non-food items for 5,000 people, and enough supplies for 260,000 medical procedures", OCHA said in a statement.

- 'More will follow' -

UN Secretary-General Antonio Guterres welcomed the resumption of the "life-saving humanitarian deliveries", his spokesman Stephane Dujarric said.

"Though our humanitarian operations have continued to assist millions of people in need in northwest Syria, the Bab al-Hawa crossing has long been central to the UN's efforts to deliver aid" there, Dujarric said in a statement.

Hayat Tahrir al-Sham (HTS), a jihadist group formerly affiliated with Al-Qaeda, controls the Syrian side of the Bab al-Hawa crossing.

Following a February 6 earthquake that struck both northwest Syria and southern Turkey, Syrian authorities agreed to temporarily open two other border crossings -- Bab al-Salama and Al-Rai.

Authorisations for those two crossings were subsequently renewed and are set to expire on November 13.

However, some 85 percent of the UN aid for the rebel-held areas goes through Bab al-Hawa.

"More trucks and missions will follow in the days ahead," UN aid chief Martin Griffiths said on Tuesday.

"The UN and its partners reach 2.6 million people each month with cross-border aid," he added on X, formerly Twitter.

OCHA said that "more than 4,000 trucks with UN aid" have entered northwest Syria through the three crossings so far this year.

About three million people, the majority of them displaced, live in areas controlled by HTS, while another 1.1 million are in zones under the control of Turkey-backed groups.

Civil war erupted in Syria after President Bashar al-Assad's government crushed peaceful protests in 2011.

The conflict has killed more than half a million people and driven half the country's pre-war population from their homes.

Roughly half of Idlib province and parts of neighbouring provinces are controlled by HTS, considered a terrorist group by Damascus, as well as by the US and UN.