A letter posted to US Republican senator Roger Wicker tests positive for ricin or a similar poison, the Senate majority leader says.

FBI images show a backpack and apparent fragments of a pressure cooker as it probes the attack on the Boston Marathon that left three dead.

An earthquake of magnitude 6.8 strikes Papua New Guinea's northern coast, causing residents who feared a tsunami to seek higher ground.

Pakistan sends troops to help its citizens affected by a deadly 7.8-magnitude earthquake that struck just over the border in Iran.

A judge opens and adjourns an embezzlement case against Russian opposition activist Alexei Navalny, who says the charge is "fabricated" by the state.

China approves the merger of commodities trader Glencore and mining group Xstrata, clearing the final big hurdle in completion of the deal.

A diminutive species of human whose remains were found on an Indonesian island could have shrunk as a result of island dwarfism, researchers say.

Men should be offered a screening test for prostate cancer in their mid- to late-40s, researchers say.