In opening remarks at a climate summit press conference today, Ban urged world leaders gathered in New York "to come together decisively" in support of efforts to confront extremist groups.
The US and five Arab nations carried out airstrikes against targets of the Islamic State group in Syria yesterday and early today for the first time, using land- and sea-based US aircraft as well as Tomahawk cruise missiles launched from two Navy ships in the region.
"I welcome the international solidarity to confront this challenge," Ban said.
Ban said that although the strikes were not carried out at the direct request of the Syrian government, authorities were informed beforehand.
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Damascus has said the US informed it that the strikes were coming.
"I also note that the strikes took place in areas no longer under the effective control of that government," Ban said.
"I think it is undeniable, and the subject of broad international consensus, that these extremist groups pose an immediate threat to international peace and security," he added.