THE HAGUE, Netherlands -- As Russia consolidated its hold on Crimea, raising its flag over seized military bases and detaining ousted Ukrainian commanders Sunday, President Barack Obama and his European allies prepared to meet in this Dutch city in an effort to develop a strong, united response despite their diverging interests in dealing with the Kremlin.
After Russia's invasion of Crimea and the lightning annexation of the peninsula by President Vladimir Putin last week, Mr. Obama's decision to convene the leaders of several European countries, along with Canada and Japan, brought the nations -- once again the Group of Seven, without Russia -- together for the first time since the crisis in Ukraine upended the stability and security of Europe.
Susan Rice, Mr. Obama's national security adviser, acknowledged that the president's weeklong trip, including a meeting Thursday with Pope Francis and a Friday stop in Saudi Arabia, would be overshadowed by Ukraine and the need to press for Western unity. Ms. Rice expressed confidence that today's meeting would "deepen" coordination.
But as the United States ratchets up economic sanctions against Russia, it may prove difficult for Mr. Obama to bring along his European allies, who are more economically intertwined with Russia and ended their own summit meeting Friday with no detailed mention of tougher sanctions.
A central question seems to be whether Western unity is more than a veneer of principled language and so-far mild sanctions, which, in the absence of any hint of a military response, has made the West seem powerless.
"It will expose the limitations within the European Union," said Michael Geary, an assistant professor of modern Europe at Maastricht University in the Netherlands, noting that the bloc needs consensus among 28 member states that have disparate ways of dealing with Russia.
NATO and the European Union have been shocked but seem galvanized by Russia's abrupt abandonment of the rules of cooperation and territorial integrity that have governed East-West relations for decades.
As the West has struggled to respond cohesively, Russia has moved assertively to establish control in Crimea. On Sunday, a base in Belbek was eerily quiet just 24 hours after it was seized in a dramatic incursion by Russian special-forces troops and two armored vehicles.
A commander of the base, Yuli Mamchur, was apparently being held along with other base leaders in Sevastopol, somewhere near the headquarters of Russia's Black Sea Fleet, said his wife, Larisa Mamchur. She added that most Ukrainian personnel there had been sent home to pack and prepare for relocation to mainland Ukraine.
"The people are crying," Larisa Mamchur said. "They are sad."
Although there were still scattered pockets of Ukrainian resistance across the peninsula Sunday, it was clear that Russia was quickly locking down. Ukrainian military officials in Crimea said bases continued to fall and that the Russian military had also detained a navy captain from a base near Sevastopol.
Even as Russian forces were storming two bases Saturday in Crimea, the Kremlin agreed to allow monitors from the Organization for Security and Cooperation in Europe to start a six-month mission in Ukraine -- though not in Crimea. The move seemed intended to ease fears that Russian forces would push into eastern or southern Ukraine.
But Mr. Putin's recent record of first coy, then bold moves has put Mr. Obama and his European allies on guard, even as they have struggled to coordinate. Caught flat-footed by the initial infiltration of Crimea, the United States seems increasingly alarmed about the 20,000 Russian troops that have massed on the border with eastern Ukraine.
Mr. Obama's sanctions, announced last week, were aimed at sowing pain among members of a Russian economic and political elite who owe their wealth and loyalties to Mr. Putin. But the sanctions were also targeted to minimize disruption to the global economy and to avoid further jeopardizing already meek Russian cooperation on issues like the war in Syria, Iran's nuclear program, the Middle East and North Korea.
For European countries, the risk of wider conflict with Russia is even graver. Britain hosts Russian billionaires and their money; Germany gets about one-third of its energy from Russia and sells it machinery and cars; France is in the process of delivering sophisticated attack ships to the Kremlin; and Italy depends on Russia for some 28 percent of its energy.
Canada's Prime Minister Stephen Harper on Saturday became the first G-7 leader to visit Ukraine since the crisis erupted. Japan has an interest in whether China -- whose president, Xi Jinping, arrived on his first European tour this weekend -- draws closer to Moscow or even secures Russian energy supplies in the event that the Kremlin cuts off Western Europe.