Russia has shown no change in behavior or policies to embrace U.S. President Donald Trump's offer of better relations or cooperation in fighting Islamist militants, Reuters quoted U.S. officials and lawmakers as saying. Trump's latest overture was delivered by Vice President Mike Pence on Saturday to a security conference in Germany held amid European worries over U.S. commitment to the continent's security and an uproar over former national security adviser Mike Flynn's contacts with the Russian ambassador to Washington. "Know this: the United States will continue to hold Russia accountable even as we search for new common ground, which, as you know, President Trump believes can be found," Pence told the Munich Security Conference in the administration's first major foreign policy address. Russia, however, has stepped up provocative actions by staging dangerous low-level fly-bys of a U.S. warship in the Black Sea this month and sending an intelligence-gathering ship to within 30 miles of the U.S. coast, said U.S. officials, lawmakers and other experts. "Running a spy ship up the coast of Connecticut is not what you'd traditionally think is an overture for cooperation," said Democratic Senator Chris Murphy, who represents the east coast state. "You've had these repeated public overtures from the Trump administration that have been met with repeated provocations by Russia," he told Reuters. To be sure, Russian President Vladimir Putin and other top officials have expressed a readiness to cooperate with the Trump administration on a range of issues, including fighting Islamist extremism. In Munich, Russian Foreign Minister Sergei Lavrov said Moscow wanted better relations with the United States. "The potential for cooperation in politics, economy and humanitarian sphere is huge. But it has to be implemented. We are open to this as much as they in the United States," he said. But Michael McCaul, a Texas Republican who chairs the House Homeland Security Committee, said: "Right now, it's all rhetoric and no action" by Putin. This was particularly true in Syria and Ukraine, he said. Having backed the government's capture of the rebel-held half of Aleppo in December with devastating air strikes, U.S. officials said Moscow had continued to focus most of its attacks on civilian areas and on Western-backed moderate rebels rather than on IS, which Russia says is its main target. Moreover, they said Russia had declined to pressure Syrian President Bashar Assad into engaging seriously in U.N.-brokered talks with Western-backed rebels on a peace plan that eventually would have Assad cede power to a national unity government. In east Ukraine, meanwhile, U.S. officials said Moscow had continued supplying heavy weapons to pro-Russia separatists amid a surge in fighting. Moscow also dismissed a White House call this month to return Crimea, the peninsula that it seized from Ukraine in 2014. In his speech, Pence called on Russia which blames Ukraine for the new bout of fighting - to implement agreements reached with Ukraine, Germany and France on resolving the conflict, "beginning by de-escalating the violence in eastern Ukraine."