An Israeli Arab family lost 18 of their relatives in Wednesday’s alleged chemical weapons attack in the suburbs of Damascus, Syria.

The Wakid family, from the northern Israeli city of Nazareth, was interviewed by Channel 2 as they were gathered in mourning for the deceased.

“We saw images of the attack like everyone else on the news,” said one of the gathered relatives, “and then a few hours we received the bad news about all the dead.” The message came from an uncle, who was the family’s sole survivor in the area.

Wednesday’s attack — which Syrian opposition forces immediately blamed on the Bashar Assad regime — killed between 136 and 1300 people, depending on different estimates.

It came as a United Nations team was on the ground in Syria investigating earlier chemical weapons use. US President Barack Obama has warned that deployment of the deadly gases would cross a “red line,” but the US response to confirmed attacks earlier this year has been minimal.

In an interview broadcast Friday, Obama called the possible chemical weapons attack this week a “big event of grave concern.” He said it was “something that is going to require America’s attention.”

British Foreign Secretary William Hague said Friday that the chances that the Syrian opposition was behind the attack were “vanishingly small.” He added, “We do believe this is a chemical attack by the Assad regime on a large scale.”

UN Secretary-General Ban Ki-moon urged the Syrian government on Friday to respond “promptly and positively” to his request for UN experts to investigate the attack.

The Associated Press contributed to this report.