Updated

Dozens of countries on Friday kicked off a large military exercise in Turkey to practice intercepting weapons before they reach a country like Iran, Turkey's neighbor.

U.S., Turkish, French and Portuguese naval ships were participating in mock drills in the Mediterranean in the largest exercise so far of the Proliferation Security Initiative, or PSI, a program started in 2003 by U.S. President George W. Bush.

Though officials have repeatedly said the exercise, which also involves scenarios of searching vehicles carrying suspected weapons materials to an airport and a land customs gate, is not aimed at any specific country, all eyes are on Iran, which is not likely to see the hosting of the nonproliferation exercise as a friendly move by its Muslim neighbor.

CountryWatch:Turkey

Countries bordering Iran, including Persian Gulf countries and Turkey, have come under increasing pressure recently to cooperate with the U.S. and pressure the Islamic Republic to give up what the U.S. says is a secret nuclear weapons program.

Analysts say the exercise will not only help increase preparedness for stopping illegal shipments that Iran could use in a weapons program, but will send the message that most of the world is united against Iran possessing those weapons.

"Iran already has most of what it needs for a nuclear weapon, but it continues to try to procure foreign components that would allow it to reach that capability faster and better," said Mark Fitzpatrick, a senior fellow at the International Institute for Strategic Studies in London.

U.S. Secretary of State Condoleezza Rice has credited PSI with successes already in intercepting shipments of missile and nuclear technology headed to Iran, but she did not elaborate on details.

PSI, however, was only one crucial part of a massive effort needed to prevent proliferation, said Charles Ferguson, fellow for science and technology at the U.S.-based Council on Foreign Relations.

"My view is that PSI fills the gaps," Ferguson said. "The borders are porous in so many different areas, that's why we can't rely exclusively on PSI ... We also need to rely on more traditional tools such as export control, IAEA inspections and diplomacy."

Ferguson said nonproliferation efforts concentrated too long on state-to-state transfers of technology and materials — until Abdul Qadeer Khan, the founder of Pakistan's nuclear weapons program, admitted in 2004 to passing nuclear technology to other countries, showing that the dangerous game also involved individuals or small groups and was getting more complex.

Pakistan shares a long border with Iran.

Officials from 34 countries will observe or participate either from a naval ship or by computer, as militaries cooperate to track, board, search and disable a hostile ship.

The exercise will begin with intelligence that weapons materials are on the way through Turkey from an imaginary country, Turkey's Foreign Ministry said.

There have been more than a dozen previous PSI exercises held in other countries, though Turkey says this one will be the largest yet.

When South Korea agreed to participate in an exercise, North Korea, also believed to have a clandestine nuclear weapons program, called it a "war crime" and threatened all-out nuclear war.