Defense Secretary Lloyd Austin briefed President Joe Biden on Saturday on US options for responding if Russia invades Ukraine, as well as options for US military movements before an invasion, according to a defense official and a senior administrative official.

Among the options presented to the U.S. military prior to an invasion were bomber flights over the region, ship visits in the Black Sea, and the movement of troops and some equipment from other parts of Europe to Poland, Romania and other neighboring countries of Ukraine.

Austin presented options to reassure NATO allies and strengthen their defenses, particularly the defenses of countries bordering Ukraine, the officials said. The aim is to show unity and strength within NATO and deter Russian aggression against allies in the region, the officials said.

As Biden weighed his options, the State Department ordered family members of embassy employees in Kyiv to leave on Sunday and allowed non-emergency diplomatic employees in Ukraine to leave. He also warned Americans not to travel to Ukraine or Russia, citing the possibility of Russian military action.

Ukraine criticized the movement withdraw families of diplomats as ‘premature’, while US allies were split on whether to immediately follow America’s lead, with the UK doing so but the European Union saying they won’t not at the moment.

Biden was at the presidential retreat in Camp David, Maryland, and Austin briefed him via secure video teleconference. Chairman of the Joint Chiefs of Staff, Army General Mark Milley, also attended the conference. Typically, the secretary briefs the president, and then the president provides more operational details.

Some details of the briefing have already been reported by The New York Times.

Air Force Gen. Tod Wolters, commander of U.S. European Command and Supreme Allied Commander Europe, has been planning options for weeks, the defense official and senior defense official said. ‘administration. Wolters has the authority to move some forces around his theater, but he is keeping Austin and military leaders informed given the severity of the situation, officials said.

The briefing for Biden included the latest reports that the Russian military has been steadily building up its forces around Ukraine, officials said.

Another defense official said Russian President Vladimir Putin continues to add more military units and deploy forces to border areas around Ukraine. “He’s getting stronger, literally day by day,” the defense official said.

Officials would not say whether Biden has endorsed any moves. The senior administration official said some troops and resources could be repositioned “in the coming days.”

Meanwhile, NATO said Monday morning it was putting additional forces on standby and sending more ships and fighter jets to Eastern Europe.

“The United States has also made clear that it is considering increasing its military presence in the eastern part of the Alliance,” the alliance said in a statement.

“NATO will continue to take all necessary measures to protect and defend all Allies, including strengthening the eastern part of the Alliance. We will always respond to any deterioration in our security environment, including by strengthening our collective defence,” said NATO Secretary General Jens Stoltenberg.

Also on Monday, the US military and NATO begin exercise Neptune Strike ’22, which includes training with NATO allies for capabilities that could be used against Russia. As part of the exercise, the strike group from the aircraft carrier USS Harry S. Truman will conduct long-range strike training and anti-submarine warfare training from the Mediterranean.

Pentagon press secretary John Kirby said the exercise is “designed to demonstrate NATO’s ability to integrate the high-end maritime strike capabilities of an aircraft carrier strike group, to support deterrence and defense of the alliance”.