The latest reports of senior nuclear scientists defecting from Iran to the West have caused considerable embarrassment and concern to the regime in Tehran.

The reports first broke in Londown-based newspaper Al-Sharq al-Awsat, and were followed up in the Iranian media.

The reports suggest that at least one scientist, Shahram Amiri, who worked on nuclear research and development, defected several months ago to the west during the hajj pilgrimage in Saudi Arabia.

One more person, whose identity and specialization remains unclear - he may have been a scientist or held another key position in Iran's nuclear program - may have also defected, this time during a visit to Georgia.

It is also not yet clear what types of information the defectors had access to, or to what extent they had important positions in the Iranian nuclear program.

However, the fact that Iran's Foreign Minister, Manouchehr Mottaki accused the United States of involvement in the disappearance of Amiri, and of Saudi Arabia of responsibility for his fate, suggests that the reports are well founded.

These defections are added to the most important one in years: In 2007 the deputy Defense Minister and a senior officer in the Revolutionary Guard, Ali Askari, defected to the West. Askari had access to the highest levels of classified information in the Iranian regime.

These defections, and possibly others that have not been publicized, are indications of the ongoing shadow war between Western intelligence agencies and the security and intelligence services of Iran.

Western governments consider Iran's bid to achieve nuclear weapons capability and its support for terrorist groups like Hamas, Hezbollah and Al-Qaida, a threat to international peace and stability. As such, Western intelligence agencies, including those of the United States, Britain, Germany and France, are involved in a massive effort to collect as much data as possible on these Iranian activities.

In recent years, espionage has been conducted with the intensified use of specialized satellites, a field in which the United States has the technological and numerical lead.

Nonetheless, in spite the technological possibilities for gathering intelligence, the ability to have access to human intelligence, agents and spies, remains unrivaled. Every intelligence service seeks to gain access to such persons, preferably situated as deep as possible in the enemy organizations.

As such, defections are not necessarily considered a success but a last resort, and it usually stems from an agent feeling that he has been compromised. But defectors who had not been agents, irrespective of the information they can provide, constitute a major psychological blow to the enemy.