High-stakes diplomacy continued on Friday in a bid to avert a war in Eastern Europe. The urgent efforts come as 100,000 Russian troops are massed near Ukraine’s border and the Biden administration worries that Russian President Vladimir Putin will mount some sort of invasion within weeks.

Here are things to know about the international tensions surrounding Ukraine.

PENTAGON LAYS OUT MILITARY OPTIONS

Defense Secretary Lloyd Austin said Friday the buildup of Russian forces along Ukraine’s border has reached the point where President Vladimir Putin now has a complete range of military options, including actions short of a full-scale invasion.

“While we don’t believe that President Putin has made a final decision to use these forces against Ukraine, he clearly now has the capability,” Austin told a Pentagon news conference.

Austin said Putin could use any portion of his force of an estimated 100,000 troops to seize Ukrainian cities and “significant territories” or to carry out “coercive acts or provocative political acts” like the recognition of breakaway territories inside Ukraine. 

Austin spoke alongside Army Gen. Mark Milley, chairman of the Joint Chiefs of Staff, in a news conference that marked a subtle shift in the administration’s approach to public communications about the Ukraine crisis, which until now has focused on the the diplomatic efforts.

Milley said Russian forces near Ukraine include not only ground troops and naval and air forces but also cyber and electronic warfare capabilities, as well as special operations forces. But he also noted that Ukraine’s military has improved significantly over the past several years, adding, “If Russia chooses to invade Ukraine, it will not be cost free, in terms of casualties and other significant effects,” Milley said.