WASHINGTON (Reuters) - U.S. forces have succeeded in finding key fugitives in Iraq -- Abu Musab al-Zarqawi being the latest -- but face bigger obstacles in catching al Qaeda leader Osama bin Laden, former Taliban chief Mullah Omar and other wanted men.
"If you don't know where he is, then you don't know where he is," Defense Secretary Donald Rumsfeld said of bin Laden during a December trip to Pakistan, whose lawless, mountainous tribal areas, experts think, may be where bin Laden is hiding.
Bin Laden, responsible for the Sept. 11 attacks on the United States that killed around 3,000 people, has eluded U.S. forces in Afghanistan, as have al Qaeda's second-in-command, Ayman al-Zawahiri, and one-eyed cleric Omar.
Defense analysts noted the United States has devoted far more manpower and resources to Iraq -- currently 131,000 troops, compared to 22,000 in Afghanistan -- and is better able to gather intelligence there.
They also argued that for political reasons -- not wanting to destabilize its ally Pakistan -- the United States has been unwilling to send forces into Pakistani tribal areas abutting the Afghan border that may provide sanctuary for bin Laden.
"It's nearly five years since the Sept. 11 attacks, and yet the masterminds of the plot -- Osama and Zawahiri -- are still at large," said Lexington Institute analyst Loren Thompson. "We have sent extremists around the world the signal that you can attack America and survive."
U.S. officials on Thursday said Zarqawi, al Qaeda's leader in Iraq, died on Wednesday in a bombing raid near Baquba. In December 2003, U.S. forces captured former Iraqi President Saddam Hussein in an underground "spider hole" at a farmhouse near his hometown Tikrit. In July 2003, U.S. forces killed Saddam's once-powerful sons Uday and Qusay in a raid in Mosul.
The closest the United States came to trapping bin Laden is believed have have been in late 2003, when the al Qaeda leader had retreated to a complex of caves in the rugged border region of Afghanistan known as Tora Bora.
U.S. forces relied on Afghan militias to seal off escape routes from the mountain redoubt, but bin Laden managed to slip past them and since then he has remained in hiding, sending occasional video or audio messages to the world.
Anthony Cordesman of the Center for Strategic and International Studies said that unlike Zarqawi, who actively led an insurgency, the role played by bin Laden and Zawahiri was less hands-on.
"They've become symbols. They're not directly involved in operations. They're not leading," Cordesman said. "So they have a very different level of visibility and a very different kind of intelligence trail from someone like Zarqawi."
Army Lt. Gen. Karl Eikenberry, top U.S. commander in Afghanistan, said last month finding bin Laden is "a commitment that we maintain every day, and we will not rest until we find and capture or kill bin Laden."
Rumsfeld said in December bin Laden is "probably spending a major fraction of his time trying to avoid being caught," and doubted he was able to operate sufficiently to command al Qaeda operations worldwide.
Charles Pena, a senior fellow with George Washington University's Homeland Security Policy Institute, said the Pentagon transferred key special-operations personnel and assets to Iraq from Afghanistan ahead of the Iraq invasion in 2003 that could have been vital in the hunt for bin Laden.
Pena said the United States has focused more on Iraq than al Qaeda in recent years with President George W. Bush describing Iraq as the "central front" in the "war on terror."
"That's how you avoid the embarrassment of not having captured or killed the man who was responsible for 9/11," Pena said.