Simferopol, Ukraine (CNN) -- Hostilities intensified in Crimea on Saturday as Ukrainian officials accused pro-Russian forces of armed aggression and President Barack Obama rounded up world leaders to demand Russia "de-escalate the situation." Obama called British, French and Italian leaders and hosted a conference call with the presidents of Lithuania, Latvia and Estonia, the White House said. "All of the leaders agreed on the need for Russia to pull its military forces back to their bases, allow for the deployment of international observers and human rights monitors to the Crimean peninsula, and agree quickly on the formation of a contact group that could lead to direct dialogue between Ukraine and Russia to de-escalate the situation and restore Ukraine's sovereignty and territorial integrity," a White House statement said.
@highlight
NEW: John Kerry tells Russia its continued escalation "would close ... space for diplomacy"
@highlight
Obama rounds up world leaders to demand Russia "de-escalate" crisis
@highlight
Russian troops seized a Crimean border control point, Ukraine border service says
@highlight
Amid disturbances, Poland evacuates its consulate in Sevastopol, Crimea
pro-Russian
Meanwhile, Ukrainian officials charged that @placeholder forces comprised of 100 armed men reportedly took control of a military office in the Crimean regional capital, Simferopol.
Crimean
Crimean
Meanwhile, Ukrainian officials charged that pro-Russian forces comprised of 100 armed men reportedly took control of a military office in the @placeholder regional capital, Simferopol.
Russia
Russia
Russia
Russia
Russia
Russian
Armed, masked men were at the entrance, and @placeholder flags were being painted on the gates.
Ukraine
Ukrainian
Ukraine
Ukraine
Ukraine
@placeholder will continue down a diplomatic path, he said, and will not respond to Russian "provocations."
Simferopol
In @placeholder, women voiced opposition to the pro-Russian Crimean government and advocated the peninsula remaining as part of Ukraine.