Maine Sens. Susan Collins, a Republican, and Angus King, an independent who caucuses with Democrats, are seen in this April 2018 file photo. Credit: Andrew Harnik / AP

Maine’s U.S. senators warned on Friday that Russia is trying to provoke conflict while Congress negotiates sanctions aimed at deterring an invasion of neighboring Ukraine.

Members of Congress received a classified briefing on the situation in Ukraine this week as President Joe Biden sent additional troops to eastern Europe amid concern about a “false flag” event designed to incite confrontation. After the briefing, Sens. Susan Collins and Angus King expressed concern about Russia’s plans while pointing to bipartisan work on sanctions.

Russia, which annexed the Crimea region of Ukraine in 2014, has denied it is planning to invade the country despite amassing more than 100,000 troops along the Ukraine border this winter. U.S. intelligence reports disclosed Thursday also indicated Russia was planning to stage a fake video of a mass casualty event allegedly perpetuated by Ukraine to justify military action.

“The signs are all pointing toward an invasion,” Collins said Friday. “I still am hopeful that the diplomatic efforts and the efforts to keep the NATO alliance unified and resolute will deter Russia, but it is difficult.”

Diplomatic talks continue, although the U.S. and its allies rejected Russian demands aiming to reduce the influence of NATO in eastern Europe. Russia has characterized NATO, a military alliance that includes the U.S. and most western European nations, as the aggressor.

The U.S. has also continued to provide defensive military assistance to Ukraine, as well as technical assistance after cyberattacks allegedly perpetrated by Russia brought down Ukrainian government websites last month. Officials have also warned of harsh sanctions if Russia mounts an invasion. But the Senate is still debating the scope of sanctions as well as flexibility for the Biden administration in implementing them, Politico reported Thursday.

Collins, a Republican, said she thought the Senate should have brought a sanctions bill to the floor this week to send a signal and punish Russia for earlier cyberattacks. But she said negotiators from the Senate Foreign Relations Committee have indicated they are “at the 1-yard line” as they seek to resolve differences about the timing and order of sanctions.

“There’s widespread agreement that you do what has been called the ‘mother of all sanctions’ after the invasion,” she said. “But the question is, ‘How much do you do before in an attempt to deter?’”

A sticking point in the sanctions debate has been Nord Stream 2, a pipeline set to begin supplying gas to Germany from Russia. All Senate Republicans as well as a few Democrats voted in favor of sanctioning it last month, but the White House balked, saying such a move could anger European allies. Senators indicated Friday the pipeline would not be immediately subjected to sanctions under a bipartisan deal, Politico reported.

King, an independent who caucuses with Democrats, said in a Friday statement that he was prepared to continue bipartisan discussions on sanctions so Russia could see the “clear costs we are prepared to impose” if its leaders chose to invade Ukraine.

“The United States and its allies will continue to seek a peaceful resolution to the growing crisis, but we will not be intimidated into ignoring Russia’s efforts to infringe on Ukrainian sovereignty,” King said.