Separatists are holding public buildings in Ukraine, saying they need more assurances about security before complying with an international deal.
The US president tells his Russian counterpart his political strategy is a generation out of date.
Major industrialised nations have warned Moscow of tougher economic sanctions if it goes beyond the seizure of Crimea.
The gold price recovered from a four-week low as G7 leaders threatened further sanctions against Russia over its annexing of Crimea.
The US and its G7 allies will gather next week at the Hague to consider a further response to Russia's attempt to absorb Ukraine's Crimea region.
The US and EU have imposed sanctions, including asset freezes and travel bans, on a small group of officials from Russia and Ukraine.
Leaders of the G7 economies have told Russia to stop its work on a referendum in Ukraine's Crimea region or face action.
Pro-Russia troops have used gunfire in seizing a Ukraine military base, while Nato has declared early-warning flights around the east.
Arseny Yatseniuk says the announcement to invade Ukraine made by Russia's Vladimir Putin was not a threat, but "the declaration of war to my country".
The US president has warned Russia's head of state against military action in Ukraine after its new leaders accused it of deploying troops in Crimea.
Barack Obama's ascent to power had meaning, but now his interventions are too rare and too piecemeal to constitute a narrative, writes Gary Younge.
Financial issues may resonate more when voters see a change in their living or working conditions, writes Lynley Donnelly.
This week, the DA has march drama, Zwelinzima Vavi threatens to sue Cosatu, France and the US get cozy, and an exhibition is plagued by disagreements.
The White House has filled Michelle Obama's seating area at the State of the Union address with people who represent issues important to her.
President Salva Kiir's government and the rebels backing Riek Machar have signed a ceasefire deal, a "critical first step" in peace negotiations.
Obamacare allies are pushing the White House to name a chief executive to run its health insurance marketplace and allay the concerns of insurers.
We take a look at some of the high and low points of Mandela's memorial, including Barack Obama's speech, booing crowds and Desmond Tutu's reprimand.
The US mission to SA says a fascination with a group "selfie" featuring Barack Obama should not be allowed to distract from honouring Nelson Mandela.
British Prime Minister David Cameron has laughed off criticism that he had acted inappropriately by taking a "selfie" at Mandela's memorial service.