LONDON -- Hoping to prevent a fifth terrorist strike, Jewish and Israeli organizations around the world tightened security Thursday.


Armed police guards kept a 24-hour watch at more than 100 sites in Britain following car-bomb attacks at two sites in London this week that injured at least 19 people. A bomb blew up part of the Israeli Embassy on Tuesday, and 13 hours later a Jewish charity building in North London was targeted.


At least 95 people were killed in an explosion July 18 at a Jewish cultural center in Argentina, and the bombing of a commuter plane the next day in Panama killed 21 people, including 12 Jews.


Israeli Foreign Minister Shimon Peres again accused Iran of orchestrating the four attacks in Argentina, Panama and Britain in the last 10 days.


"There are people who want to murder peace and their main headquarters is in Tehran," Peres told Israel radio.


Argentine officials have detained two Iranians for questioning in connection with the bombing. The two, a man and a woman, were not identified. Argentina has also called its ambassador to Iran back to Buenos Aires for consultations. Iran has vehemently denied any involvement with the series of bombings, and has blamed Israel itself for engineering the attacks in order to "defame Islam."


After discussing the violence at a weekly session Thursday, Israel's cabinet said it "condemns the spilling of blood of innocent civilians and declares it will act and assist in apprehending the assailants and in punishing them."


Across Europe security measures were bolstered. Police in Bonn checked identity papers of people passing near the Israeli Embassy, where barriers were up and security guards and German police patrolled. Similar precautions were taken at the Israeli consulates in Frankfurt and Berlin, German police said.


Leaders of the 42,000-strong German Jewish community called on the government to increase security at synagogues and Jewish centers across the country, said Michael Friedman, a Frankfurt-based Jewish leader.


In London, yellow cones blocked cars from parking outside The Jewish Chronicle newspaper and a policeman patrolled the street around the clock. Security was also tightened at the building which houses the Board of Deputies of British Jews, the chief rabbi and the Jewish Museum.


In Paris, steel barriers were placed outside certain buildings with Jewish or Israeli connections to prevent parking.


In Japan, Belgium, Spain, Austria, Denmark and the Philippines, authorities patrolled Jewish community buildings, synagogues and Israeli embassies.


A spokesman at the Israeli Embassy in Moscow said "strict security measures" were in effect both inside and outside the embassy.


In New York, concrete barriers were put up outside the Israeli Consulate and an Israeli office building after police said they received a threat.