Merkel is hoping to secure commitments from her G7 guests to tackle global warming ahead of a major United Nations climate summit in Paris in December.
The German agenda also foresees discussions on global health issues, from Ebola to antibiotics and tropical diseases. But Ukraine took center stage on Sunday, with U.S. President Barack Obama calling for "standing up to Russian aggression".
The leaders want Russia and Ukraine to comply with a Feb. 12 ceasefire agreed in the Belarus capital Minsk that largely halted fighting in eastern Ukraine between pro-Russian separatists and Ukrainian government forces.
EU leaders agreed in March that sanctions imposed over Russia`s seizure and annexation of Crimea and detribalization of eastern Ukraine would stay until the Minsk ceasefire was fully applied, effectively extending them to the end of the year, but a formal decision has yet to be taken.
Merkel said any easing of the sanctions depended largely on Russia and its behavior in Ukraine.
European Council President Donald Tusk went further, saying: "If anyone wants to start a discussion about changing the sanctions regime, it could only be about strengthening it."
European monitors have blamed a recent upsurge in violence in eastern Ukraine on the pro-Moscow separatists. Russian President Vladimir Putin was frozen out of what used to be the G8 after Moscow`s annexation of Crimea last year.
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