BEIRUT/UNITED NATIONS – Opposition activists again accused President Bashar Assad’s forces of using poison gas in Syria’s civil war on Thursday, showing footage of an apparently unconscious man lying on a bed and being treated by medics.

The alleged attack on the neighborhood of Jobar in the capital, Damascus, comes a week after the Syrian government sent a letter to the United Nations claiming it had evidence that rebel groups were planning a toxic gas attack in the same area.

Reuters could not independently verify the footage or the claims due to security restrictions on reporting in Syria.

Activists from the opposition Jobar Revo group posted the video on YouTube of a man being treated with oxygen and being injected by medics. A voice off-screen said Thursday’s date and that there was “a poison attack in Jobar.”

Another opposition group, the Syrian Revolutionary Coordinators Union, said that all those affected by the gas were “in a good condition.” There has been on-and-off fighting between rebels and government forces in Jobar this year.

Meanwhile, in a letter dated March 25 and circulated by the United Nations this week Bashar Ja’afari, Syria’s U.N. envoy, said his government had intercepted communications between “terrorists” that showed a man named Abu Nadir was secretly distributing gas masks in the rebel-held Jobar area.

Ja’afari said in the letter addressed to U.N. Secretary-General Ban Ki-moon and the U.N. Security Council that this information “confirms that armed terrorist groups are preparing to use toxic gas in Jobar quarter and other areas, in order to accuse the Syrian government of having committed such an act of terrorism.”

“The authorities also intercepted another communication between two other terrorists, one of whom is named Abu Jihad,” Ja’afari said. “In that communication, Abu Jihad indicates that toxic gas will be used and asked those who are working with him to supply protective masks.”

A senior Western diplomat, speaking on condition of anonymity, said of the Syrian intelligence, “I don’t give any credence to that.”

A U.N. inquiry found in December that sarin gas had likely been used in Jobar in August and also in several other locations, including in the rebel-held Damascus suburb of Ghouta, where hundreds of people were killed. The inquiry was only looking at whether chemical weapons were used, not who used them.

The Syrian government and the opposition have accused each other of using chemical weapons, and both have denied it.

Assad agreed to destroy his chemical weapons stockpile following global outrage over the large-scale sarin gas attack in Ghouta in August. The gas attack sparked a U.S. threat of military strikes, which was dropped after Assad’s pledge to give up chemical arms.

But the Syrian government, locked in a 3-year-old war with rebels seeking to overthrow Assad that has killed more than 150,000 people and caused millions to flee, failed to meet a Feb. 5 deadline to move all of its declared chemical substances and precursors, some 1,300 tons, out of the country.

Syria has since agreed to a new timetable to remove its chemical weapons by late April.

Syria is responsible for transporting the chemicals to its Mediterranean port of Latakia, where they will be shipped abroad for destruction.

In a separate letter to Ban and the Security Council, Ja’afari also warned that “armed terrorist groups continue to threaten and carry out terrorist attacks against chemical weapons facilities and the chemical substances.”

The senior Western diplomat said: “I don’t think there’s any evidence that any of the groups have any interest in attacking the convoys.”