A 22-year-old man in Tucson, Arizona, killed four people and seriously wounded the local Democrat Congresswoman, Gabrielle Giffords, with gunshots.
At a memorial service President Obama pleaded for more civility in public discourse to minimise political tensions.
In Spain the Basque separist organisation ETA announced a permanent cease fire but the government said there was nothing new in the announcement.
A Russian report said that the air crash that killed Poland's president Kaczynski and 95 senior political figures was caused by pilots who yielded to pressure to land in thick fog.
The first by-election in Britain since the May 2010 election was won by Labour with the government's coalition partners, Liberal Democrats and Conservatives. in second and third places respectively.
After several weeks of public demonstrations against unemployment and rising food prices the president of Tunisia relinquished power and left by air for exile in Saudi Arabia.