Government officials are worried that more terrorist attacks on U.S. interests, either at home or abroad, may take place if and when the United States and its allies retaliate for the attacks of Sept. 11, Fox News has learned. 

Fox News has also learned that two past attempts to capture or kill Usama bin Laden, prime suspect in the destruction at the World Trade Center and the Pentagon that killed an estimated 7,000 people, foundered because of overseas political problems. 

A U.S. official said the chances of an additional terrorist strike were "very high" and that intelligence officials are "equally concerned about a terrorist strike occurring prior to or immediately after the U.S. retaliates against bin Laden." 

The official said information indicates another possible attack on U.S. soil and possible attacks on U.S. interests in the Persian Gulf region, including U.S. military bases and embassies there. 

European and American investigators are now "certain" that plots existed to blow up four major targets in Europe: the European Parliament in Strasbourg, France; NATO headquarters in Brussels, Belgium; the U.S. Embassy in Paris; and the U.S. consulate in Marseilles, France, Fox News has learned.

Investigators say they have arrested 30 people on conspiracy charges in Belgium, Britain, France and the Netherlands. Additional suspects have been arrested in the United Arab Emirates. Investigators say there are definite links to bin Laden and his Al Qaeda organization. 

The four European nations have agreed to expedite extradition so the suspects can be delivered to the U.S. for questioning. If it is determined that the suspects were involved in the Sept. 11 attacks, the European countries have already agreed they will not make their customary objections to the death penalty. 

Investigators discovered during secret questioning that the conspiracy had at least 50 plotters. The search for additional conspirators is focused on Germany, Italy and Belgium. 

Two suspects from the UAE were extradited to France over the last two days. One told investigators he had taken a pledge of allegiance to bin Laden and had agreed to carry out a suicide bombing. His lawyer now says his clients' comments were misinterpreted. 

U.S. intelligence agencies have, in the past two weeks, detected shipments and money being funneled by Al Qaeda to an Islamic extremist group in Somalia, Fox News has learned. The shipments included grenade launchers and shoulder-fired anti-aircraft missiles. 

The official said at this point it is still too early to say whether Al Qaeda is setting up an alternative base in the East African country. But U.S. officials believe if bin Laden were to relocate, Somalia would be a likely place and is on the short list of locations. 

Eighteen U.S. soldiers were killed by mobs in Somalia in 1993, as an international attempt to head off famine caused by civil war collapsed. Bin Laden is now thought to have been involved in those deaths. 

Fox News has also learned that two attempts to either capture or kill bin Laden in 1996 and 1999 failed, information corroborated by articles in Wednesday's Washington Post. 

In 1999, the CIA trained and equipped about 60 commandos of the Pakistani intelligence services to go into Afghanistan to "get" bin Laden, a U.S. official said. The government of Prime Minister Nawaz Sharif was cooperating with the Clinton Administration on the plan, but when Sharif was overthrown in a military coup led by current Pakistani President Gen. Pervez Musharraf, the change of leadership caused the operation to fall apart. 

In early 1996, the Islamist government of Sudan had discussions with the CIA and offered to arrest bin Laden and place him in Saudi custody. When the Saudis refused to go along with the plan, the Clinton Administration looked for grounds to indict him in U.S. courts but at that point, two years before the 1998 U.S. embassy bombings in Kenya and Tanzania, there was not a strong enough case against him. 

The Saudis did not want to accept bin Laden, a U.S. official said, because of the "internal outrage" his return would cause in their country. 

Bin Laden is the youngest son and black sheep of a large, wealthy and powerful Saudi family, and his extremist Islamism is an extension of the official Saudi austere and rigid Wahhabi interpretation of Islamic law. He was stripped of his Saudi citizenship in 1994, rendering him an essentially stateless person. 

In May of 1996, Sudan expelled bin Laden and his organization to Afghanistan, where he quickly threw his financial and military support behind the emerging clerical militia, the Taliban. With his and Pakistani help, the Taliban quickly gained control of most of the country. 

U.S. officials have gathered information about a new group of Islamic radicals in Iran with ties to Usama bin Laden, Fox News has learned. 

The information raises questions about Iran's tolerance and encouragement of bin Laden, previously thought to be an enemy of Teheran. 

Sources say the "Jund al-Islam" (Soldiers of Islam) was created on Sept. 1 from a number of factions that deserted the Islamic Unity Movement of Kurdistan (PUK) in Iran. Teheran has been involved in talks mediating disputes between the PUK and the Soldiers of Islam for two weeks. 

Authorities say the Soldiers of Islam declared a jihad against "sinister Jews and Christians" on the day it was formed. 

Intelligence sources say as many as 35 members of the group trained at Al Qaeda bases in Afghanistan and they are currently funded by Usama bin Laden. 

On Sept. 23, the Jund al-Islam allegedly killed numerous Iraqi Kurds living in a village on the northeastern Iranian border with Iraq. The PUK claims the Iranian government helped the Soldiers of Islam attack Kurdish civilians. 

Full-scale war nearly broke out between the Shi'ite Islamic revolutionary government of Iran and the Taliban after several Iranian diplomats were executed when the Taliban took the northwestern Afghan town of Mazar-e-Sharif from the Iran-supported Northern Alliance. 

Iran, with one of the world's highest rates of heroin addiction, has also been using troops to battle drug-smuggling gangs along the southern Afghan border thought to be supported by the Taliban. 

Nevertheless, right-wing factions within the deeply divided Iranian leadership are thought to be sympathetic to Usama bin Laden's cause. That division was underlined when supreme spiritual leader Ayatollah Ali Khamenei, successor to the late revolutionary leader Ayatollah Khomeini, called American plans for an international coalition against terrorism "disgusting" and declared that his country would in no way cooperate with efforts against bin Laden. 

In contrast, popularly elected President Mohammad Khatami, leader of the liberal faction, condemned the terror attacks and offered sympathy to America as young people in the streets of Tehran marched in a candlelight vigil for the victims at the World Trade Center and the Pentagon. 

Fox News' Rita Cosby, Carl Cameron and Paul Wagenseil contributed to this report