Key evolutions of a warning:
Oct 3 - The United States and Britain warned their citizens of an increased risk of terrorist attacks in Europe, with Washington saying al Qaeda might target transport infrastructure. Western intelligence sources said militants in hide-outs in northwest Pakistan had been plotting coordinated attacks on European cities.
Oct 5 - French police arrested 12 people in early morning raids the interior minister said were directly linked to a campaign to counter an elevated terrorism threat in Europe. France was on high alert after seven hostages, including five French citizens, were kidnapped by the North African wing of al Qaeda last month.
Oct 5 - The French government warned citizens travelling to Britain to exercise caution due to a very high risk of terrorist action in the country that could target public transport and tourist sites.
Oct 6 - Suspected al Qaeda militants attacked two Western targets in Yemen, firing a rocket at a senior British diplomat's car and killing a Frenchman at a gas and oil installation.
Oct 17 - French Interior Minister Brice Hortefeux said France had been warned by Saudi Arabia that al Qaeda was targeting Europe and especially France.
Oct 27 - A Virginia man who allegedly believed he was helping al Qaeda plan bombings at Washington area Metrorail stations was arrested, the U.S. Justice Department said.
Oct 28 - Britain's top spy, in the first public speech by a serving UK espionage chief, said terrorists might hit the West again "at huge human cost" but nuclear proliferation by states was a more far-reaching danger.
The Jewish organizations in the area and from the US are under alert.
Several high level meetings are expecting to be held today, analyzing the impact and the emergency measures to be taken immediately.