At least 71 people were killed and 325 others wounded in rebel-held Eastern Ghouta after the Syrian government carried out a series of airstrikes and artillery bombardments, the UK-based Syrian Observatory for Human Rights said Monday.

Sixty-two of the victims were civilians, including nine children and five women. Nine militants were killed, the group said of the attacks near Damascus over a 24-hour period.

CNN could not independently verify the claim.

The Eastern Ghouta area has been surrounded by Syrian forces for more than four years, with the siege intensifying last May when government forces conducted a large-scale offensive.

It was supposed to be one of the "de-escalation zones," according to the peace agreement struck by Russia, Turkey and Iran in May 2017.

About 400,000 Syrians have been killed since the conflict erupted in 2011, according to the United Nations. As many as 5.4 million Syrians have left their country, the UN Refugee Agency said, and 6.1 million are displaced from their homes but still inside Syria. The UNHCR High Commissioner, Filippo Grandi, calls the situation in Syria "the biggest humanitarian and refugee crisis of our time."

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