"This is a matter of very considerable concern. We are asking MEPs, together with their families and staff, to be alert in their homes, their offices in the European Parliament and in their constituencies," he said.
"We strongly condemn these acts which amount to a criminal conspiracy against democracy," he added.
He was speaking after booby-trapped letters sent to two Euro-lawmakers, including the head of the assembly's biggest party, exploded, although nobody was injured. Three or four other suspicious letters were also investigated.
Four EU institutions
The incidents follow devices sent to the heads of four other EU institutions over the Christmas holidays. All four were sent from the northern city of Bologna, as were at least two of Monday's suspect packages.
EU officials had already announced unspecified strengthening of security after the attacks last month. The EU assembly's leaders called a rapid review of those measures after the new incidents.
"As a parliament we will intensify the measures which have already been taken to put in place, appropriate security and scanning procedures," said Cox.
"As a parliament we will intensify the measures which have already been taken to put in place, appropriate security and scanning procedures"
European Parliament head
"We are offering our full co-operation to the police and security authorities and we will insist that this be acted on with speed and determination," he added.
High ranking anti-terrorist police officers from several countries met on Monday at the Italian interior ministry amid mounting concern over the orchestrated letter bomb campaign against EU bodies.
Investigators from France, Greece and Spain - countries all affected in the past by anarchist unrest - took part in the meeting, which was chaired by Italian police chief Gianni de Gennaro, an interior ministry spokeswoman said.
The desk where the letter bomb
to an EU lawmaker was opened
The meeting had been planned long ago but is set nonetheless to focus on the campaign of letter bombs, most of which were sent from the Italian city of Bologna.
The European parliament on Monday launched a rapid review of security after two booby-trapped letters sent to Euro-lawmakers exploded.
On Monday, no one was hurt when a letter sent to German Hans-Gert Poettering, head of the European People's Party, the biggest group in the EU assembly in Brussels - was opened and exploded.
Later in the day, police confirmed a "slight explosion" at the office of a British member of the European parliament. A spokesperson for Greater Manchester Police said police went to the office in the Radcliffe district of Manchester, northwest England, following a report of a "suspicious package".
A letter bomb was sent to office of
Hans-Gert Poettering in Brussels
The package is believed to have caused a slight explosion, but no one was injured, said the spokesperson.
Between 27-30 December, European Commission head Romano Prodi, European Central Bank (ECB) chief Jean-Claude Trichet, as well as the heads of Europol and the crime-fighting organisation Eurojust in The Hague were targeted by booby-trapped devices.
The four devices were identical and, according to the Italian press, contained a tract entitled "Operation Santa Claus" including anarchist symbols and signed by the Informal Anarchist Federation.