BEIRUT/AMMAN (Reuters) - The Syrian Kurdish militia YPG on Tuesday accused Islamist and other rebel groups fighting President Bashar al-Assad’s forces of shelling a mainly Kurdish residential district in the northern city of Aleppo with chemical agents.

YPG fighters have been battling the insurgents for weeks on a heavily contested frontline that includes the district and countryside near Aleppo. Many insurgents view the YPG as allies of Assad, a charge the Kurds deny. The YPG is a key ally of both the United States and Russia in the fight against Islamic State.

A statement from the command of the People’s Protection Units (YPG) said rebels operating from opposition-held parts of Aleppo had hit Sheikh Maqsoud with “chemical material believed to be phosphorus with a yellow coloring” at 1500 local time.

In a letter the YPG said it had sent to a task force monitoring Syria’s current cessation of hostilities, the Kurdish group said the shelling had come from a broad array of Syrian opposition brigades, including the Islamist group Ahrar al Sham and more mainstream rebels such as the Levant Group, Liwa 13 and Nour al Din al-Zinki.

An Ahrar al Sham spokesman was not immediately available to comment on the allegations.

Around 16 people were killed, mostly women and children, after insurgents fired dozens of rockets on the mainly Kurdish residential district on Sunday, according to Kurdish sources. [L5N16G2SY]

The Syrian Observatory for Human Rights, which monitors the civil war, said the Syrian al-Qaeda offshoot Nusra Front and hardline Islamist insurgent groups had showered the district with dozens of rockets in recent days.

Since Russia’s intervention in the Syrian conflict, government forces and their allies have been recapturing territory lost last year in many parts of western Syria, including Aleppo province.

Diplomats and analysts say the YPG fighters are taking advantage of the insurgents’ current focus on trying to fend off the government forces’ ground offensive to disrupt traffic on the main highway overlooked by the Sheikh Maqsoud district that is used by rebels to get into opposition-held areas of Aleppo.

Rebels say Kurdish snipers on the high ground in Sheikh Maqsoud have shot and killed scores of civilians in recent weeks in what they say are attacks coordinated with the Syrian army to encircle rebel-held parts of the city, a charge the Kurds deny.

Jihadist groups are outside the cessation of hostilities accord, which diplomats hope will pave the way for talks to end the five-year-long conflict, in which more than 250,000 people have been killed and around 11 million driven from their homes.