A suicide bomber killed more than 33 people gathered for new year celebrations in the province of Hasakeh, while dozens more were wounded in another blast at a separate feast.
"Initial reports suggest that two separate bombings killed and injured up to 100 persons, including women and children," the UN secretary general said in a statement following the attacks yesterday.
"These heinous attacks took place during a holiday that is customarily a time for Kurdish communities to come together to share their hopes for the new year."
Ban said he "takes note" of the allegations that IS jihadists were behind the attack, and condemned the militant group.
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"The terrorist organisation's despicable agenda includes efforts to incite sectarian and ethnic division among Syria's diverse communities. It must not be allowed to succeed," he said.
Hasakeh is a strategic province near Syria's borders with Iraq and Turkey.
The Islamic State group controls several parts of the province, while fighters from the Kurdish People's Protection Units (YPG) hold the provincial capital, which is also called Hasakeh.