The US and Russia stepped up diplomatic efforts to defuse the Ukraine crisis on Wednesday amid heightened tensions on the ground in the flashpoint area of Crimea as gunmen threatened the UN envoy.
US secretary of state John Kerry held the first direct talks with his Russian counterpart as Washington warned Moscow it risked losing its coveted G8 place over the worst East-West crisis since the end of the Cold War.
The volatile situation in Eastern Ukraine showed little sign of easing as a dozen people were hurt as pro-Russian protesters took back the regional government building in the city of Donetsk.
And in Crimea, gunmen part-seized a Ukrainian missile facility in Cape Fiolent near Sevastopol, Ukrainian officials said.
Earlier on Wednesday, the European Union unveiled an aid package worth at least 11 billion euros ($15 billion) to support Ukraine's new pro-EU leaders the day after the US announced a $1 billion loan guarantee pledge.
The West continued its strategy of combining support for the new government in Kiev with pressure on a defiant Russia to back down.
US treasury secretary Jacob Lew made clear it was also prepared to act ahead of a summit of G8 leaders in June.
"We are on a path where I think it's clear Russia cannot sit in Sochi at G8 meetings while it's pursuing the policies that it's now pursuing," Lew said.
Lavrov and Kerry were meeting for the first time since Moscow-backed president Viktor Yanukovych was ousted late last month after three months of protests which left nearly 100 dead.
In a bid to end the crisis, US President Barack Obama has outlined proposals including Russian forces returning to their bases in strategically crucial Crimea, home to Russia's Black Sea naval fleet.
Obama also wants the deployment of international observers and the start of talks between Moscow and Kiev, a US official said.
But Russia insists there are no troops from its military operating in Crimea.
"If they are the self-defence forces created by the inhabitants of Crimea, we have no authority over them. They do not receive our orders," Lavrov told reporters.
Lavrov is likely to argue that Ukraine's interim government is illegitimate and anti-constitutional, echoing Putin's comments at a press conference on Tuesday.