WASHINGTON, April 30 (Xinhua) -- The threat against Europe from Islamic State (IS) militants is worse than the threat from al-Qaida in the late 1990s, a U.S. expert said in a recent interview with Xinhua.

"I think the situation in Europe is even more dire than what was happening with al-Qaida in the 1990s," said Colin P. Clarke, an associate political scientist at the U.S. think tank RAND Corporation.

IS is not only on the march in the Middle East by taking over large swaths of land in Iraq and Syria, but also has shown its teeth through launching a series of horrible terror attacks by its terror cells all over Europe.

Last November, IS gunmen killed 130 victims in a vicious attack in Paris, France, that made headlines worldwide.

And just last month, IS struck again in Brussels, Belgium, simultaneously setting off three nail bombs -- bombs packed with nails that fly out at lighting speed and pierce through flesh -- at an airport and metro station that killed more than 30 victims.

These terror attacks reminded people of the one launched by al- Qaida, the terror group run by terror mastermind Osama bin Laden, against the U.S. homeland on Sept. 11, 2001 that killed about 3, 000 people in New York and Washington DC.

U.S. top intelligence official James Clapper said earlier this week that the Islamist radicals have cells in the United Kingdom, Germany and Italy. He made the comments just after U.S. President Barack Obama asked European leaders to step up their efforts and contribute more to the fight against IS.

Clapper has suggested that European cities such as London, Berlin or Rome could be next on IS' hit list, as carrying out such brutal attacks increases the group's relevance and helps boost recruitment efforts.

"Then, al-Qaida was using Europe as a staging ground to recruit, fundraise and build its media and logistical capabilities. The threat from IS today is ...the group seeking to conduct spectacular attacks in major European cities like Paris and Brussels," Clarke said.

One crucial question to ask, said Clarke, is what the broader support network looks like and whether there is already a support network in place that can furnish IS fighters with forged documents (such as passports), vehicles, safe houses, weapons and ingredients necessary to construct explosives.

"My instinct is that there is some semblance of a support network, but the million-dollar question is just how robust is that network and can law enforcement and security services dismantle it or at least disrupt it before it is able to strike?" he asked.

Asked about the threat to the U.S. posed by IS, Clarke said the temptation to strike the U.S. by the radical group is big.

"For certain, we know that the chances (of an attack on the U.S. ) are not zero," Clarke said.

In fact, IS has already threatened that it would "fly its flag over the White House."

"IS has already articulated a desire to strike the United States, and attacking a city like New York or Washington DC would obviously be huge propaganda coup for the group, even if the attacks weren't extremely lethal," Clarke said.

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