WASHINGTON — The shoot-down of a Malaysian commercial airliner flying at 33,000 feet over Ukraine could dramatically broaden the Ukrainian crisis, even before it is determined who bears responsibility.

What has been a months-long shooting war between the U.S.-backed government in Kiev and Russian-supported separatists – and a war of words and sanctions between the West and Russia – now includes the deaths of nearly 300 people from a variety of countries.

Britain, which a Malaysian Airlines manifest indicated had at least six citizens aboard the aircraft, has called for an emergency meeting Friday of the U.N. Security Council. While no Americans were initially reported aboard, early information from the manifest accounted for only 233 of at least 280 passengers.

In the Netherlands, where Malaysian Airlines Flight 17 took off from Amsterdam on Thursday en route to Kuala Lumpur carrying more than 150 Dutch citizens, Prime Minister Mark Rutte rushed home from a just-begun vacation.

“I am deeply shocked,” Rutte said in a statement. “Very much is still unclear about the facts, the circumstances and the passengers.”

Other fatalities included citizens from across a wide swath of Europe, East Asia and Australia.

“This is a new element that nobody expected,” said James Collins, a former U.S. ambassador to Russia, now at the Carnegie Endowment for International Peace. “It’s one of those events . . . that can have unpredicted negative or positive consequences.”

On the negative side, it marks a clear escalation of both firepower and the willingness to use it that could draw the patrons of both sides into more overt participation on the ground, and more direct confrontation with each other.

But Collins and others suggested that the shocking nature of the shoot-down could also be a wakeup call to all involved.