Barack Obama arrives on Monday morning in the Netherlands, where he will try to gauge how far European allies are willing to go to stop Moscow from moving deeper into Ukraine after annexing Crimea.  The US president is visiting Europe for talks with fellow leaders of the Group of Seven industrial democracies, when he will try to persuade them to increase pressure on Russia.  It comes as Russian troops backed by helicopters stormed a Ukrainian naval base on the Crimea peninsula early on Monday, one of the few military facilities that was still flying a Ukrainian flag in Crimea after Russia's annexation.  First Lieutenant Anatoly Mozgovoy told Reuters on the phone from inside the base that there were shots fired and that the Ukrainian soldiers were driven away.  Ukrainian army officer First Lieutenant Anatoly Mozgovoy told Reuters by phone from inside the compound on Monday that the Russians had fired shots and the Ukrainian soldiers were unarmed. Asked if the base had been taken over, he said: "Yes."  "The invading troops were using stun grenades and also firing automatic weapons. The interior of the compound is full of Russian troops," said Vladislav Seleznyov, a Ukrainian military spokesman in Crimea.  Seleznyov said Russian forces were taking away all Ukrainian officers from the base to another location in the city for questioning.  Russian troops used armoured vehicles, automatic gunfire and stun grenades to take the Ukrainian Belbek airbase on Saturday. The Russian flag is now flying at 189 Ukrainian military bases in the Crimea.  Obama, whose trip includes visits to Belgium, Italy and Saudi Arabia, has threatened US sanctions against key sectors of the Russian economy. European allies have far closer economic ties to Russia than the United States and their still-fragile economies could face a backlash if they get tough with Moscow.  Russia provides almost a third of the EU's gas needs and some 40 percent of the gas is shipped through Ukraine.  "Europeans are committed to do something," said Jeffrey Mankoff, a Russian analyst at the Center for Strategic International Studies. "I think it'll be difficult to convince them to go anywhere near where the United States would like to go."  Russia's abrupt annexation of the Crimea region of southern Ukraine has presented Obama with an urgent foreign policy challenge, one that may weigh heavily on a second term that he would have preferred to devote to domestic affairs.  Privately, there is some doubt among US officials that Russian president Vladimir Putin can be persuaded to relinquish his grip on Crimea, where he took advantage of the ousting of pro-Moscow Ukrainian president Viktor Yanukovych to make a move.  While refusing to concede the loss of Crimea, Obama's goal in Europe is to lead an effort to isolate Russia and dissuade Putin from moving into southern or eastern Ukraine.  "Our interest is not in seeing the situation escalate and devolve into hot conflict," White House national security adviser Susan Rice told reporters. "Our interest is in a diplomatic resolution, de-escalation, and obviously economic support for Ukraine, and to the extent that it continues to be necessary, further costs imposed on Russia for its actions."  Obama has imposed sanctions on 31 people in a campaign carefully crafted to target Russian officials with links to Putin without creating a backlash against US businesses.  But officials said Obama is prepared to launch widespread penalties against key sectors of Russia's economy, such as its energy industry, should Putin move into southern or eastern Ukraine.  On Wednesday in Brussels, Obama will talk about ways to beef up Nato with Nato secretary-general Anders Fogh Rasmussen. A speech at Brussels' Palais des Beaux Arts will focus on the importance of the transatlantic alliance.  "Obviously, the situation in the Ukraine will factor heavily into his presentation. It only reinforces the need for the United States to remain committed to a strong transatlantic alliance," said Ben Rhodes, the White House deputy national security adviser.  Obama is facing pressure from Republican lawmakers to do more to bolster Nato allies near Russia, such as the Baltic nations, and quickly move to stronger sanctions.  "We need to send a message to Vladimir Putin through stronger sanctions. We need him to understand that the sanctions that we put in place can have a significant impact on his economy, that we need to deter further action from him," Republican Senator Kelly Ayotte of New Hampshire told CBS' Meet the Press.  Obama will have more on his plate than Ukraine this week. On Monday he will join allies for a nuclear security summit at The Hague and will sit down separately for talks with Chinese President Xi Jinping, their first face-to-face meeting since a G20 summit in Russia.  On Tuesday, he will participate in a three-way summit with Japanese prime minister Shinzo Abe and South Korea president Park Geun-Hye to try to defuse tensions between the Asian powerhouses ahead of an Obama visit to Asia in April.  Obama will also discuss with European leaders on Wednesday in Brussels a proposed Transatlantic Trade and Investment Partnership agreement and joint efforts to reach a comprehensive agreement with Iran to contain its nuclear program.  The European Union's ambassador to the United States, Joao Vale de Almeida, said Europeans hope the US-EU summit will be a "clear restatement of the importance of our transatlantic ties".
Russian troops storm one of last Ukrainian bases in Crimea as US president arrives in Netherlands for talks with G7 countries