Three years after the devastating Sept. 11 attacks (search), Secretary of State Colin Powell said he believes Usama bin Laden (search) is still alive and on the run.

But there's no proof of that, the diplomat acknowledged.

Bin Laden's Al Qaeda network has been smashed at the top levels, Powell said, a day after bin Laden's second in command, Ayman al-Zawahri (search), issued a new videotape that asserted the terror group would defeat the United States in Iraq and Afghanistan.

"It does have the capacity to regenerate itself," Powell said of Al Qaeda. But any future leaders are not as accomplished nor as experienced as "those who have been taken out" in the U.S. campaign that overthrew the Taliban regime in Afghanistan and the subsequent hunt for Al Qaeda operatives, Powell said in an Associated Press interview.

Other experts have, in the past, said that any terror activities that may be ongoing likely are the doings of smaller splinter groups that are acting on their own without central coordination from any one Al Qaeda leader.

The CIA's technical analysis of the 51-second tape that aired on Arabic satellite station, Al Jazeera, on Thursday has been completed, FOX News has learned, and agency analysts have a "high level of confidence" that the person seen on the tape is the man routinely described as al al-Zawahiri.

The CIA's conclusion is worded a little more strongly than usual, and officials at the agency are crediting the high quality of the video for the rapid, nearly definitive assessment.

The Saudi expatriate bin Laden, the target of Bush administration rhetoric after the attacks three years ago, largely has been dropped out of the U.S. lexicon. There was no direct mention of him at the Republican National Convention that nominated President Bush for a second term, although the commander-in-chief's record on the War on Terror was a foundation for the convention's message 

"I don't know where he is," Powell said. "I don't know his state of health. I believe he is still alive, but I can't prove that. He clearly is in hiding and he is on the run."

Powell went on: "He is not popping up on television and he is not showing himself in a way that he can be captured."

Reflecting on the three years since the Sept. 11 attacks, Powell asserted "we are safer" but "we are still in a threatening environment. There are still people who want to strike the United States."

On another issue, Powell sought to ease Russia's irritation with his suggestions that ultimately there must be political dialogue to resolve the war for independence in the rebellious province of Chechnya.

"How this problem of Chechnya will ultimately be solved is something for the Russians to work out," Powell said. "With respect to terrorist attacks against innocent Russians, we stand united with the Russians that they have to deal with this in the most powerful, direct, forceful way that they can in order to protect their citizens — the same as we are doing to protect our citizens."

Also, Powell said North Korea would seize on disclosures that South Korea had conducted experiments with enriched-uranium and plutonium, key ingredients for making nuclear weapons. "It's quite clear that these were not intended other than for academic, experimental purposes," he said.

Asked, meanwhile, if he would serve a second term as secretary of state if Bush won re-election, Powell did not rule it out. "Time will tell. We will see."

"The president and I have a very strong relationship," he added.

FOX News' Ian McCaleb and The Associated Press contributed to this report.