MELISSA BLOCK, HOST:
More now on those warnings to President Assad that Kelly mentioned about chemical weapons. Here's President Obama speaking yesterday.
PRESIDENT BARACK OBAMA: Today I want to make it absolutely clear to Assad and those under his command, the world is watching. The use of chemical weapons is and would be totally unacceptable. And if you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable.
BLOCK: That's the president yesterday at the National Defense University. The warning came after the U.S. apparently detected some activity at known chemical weapons sites in Syria. We're joined now by NPR Pentagon correspondent Tom Bowman. And Tom, what kind of activity are we talking about? Do you know?
TOM BOWMAN, BYLINE: Well, Melissa, we're not sure exactly what activity we're talking about here. There have been reports that Syria was combining certain chemical precursors to make sarin gas, basically readying weapons for use, but that idea is being knocked down by Pentagon officials. What they're saying is there's clearly stepped up activity at some sites and there are dozens of them spread around the country.
And what the Obama administration is concerned about is that the Assad regime may feel its back is up against the wall and it may lash out using these chemical weapons.
BLOCK: And that prompts the warning from the president, also from Secretary of State Hillary Clinton, an effort to make clear that Syria had better not cross that line.
BOWMAN: Right, that there would be consequences. And we're talking about the threshold being the use of chemical weapons.
BLOCK: But short of that threshold, Tom, of Syria actually using chemical weapons, there is talk now of contingency plans that the U.S. is drawing up that would prevent Syria from ever getting to that point. What are those?
BOWMAN: Well, experts and military officials I talked with say there are basically three options. The first is to try to get Syrian forces or defectors to continue maintaining security at these chemical weapon sites, basically ignore orders from the Assad regime so the government can't use these weapons. And officials I've talked with are actually considering paying off some of these forces. So that's one option.
Another is to have U.S. or allied ground forces go in. These would be small teams of U.S. special operations forces working with maybe Jordan or Turkey to secure these sites. Now, the downside is there are dozens of these sites spread all around the country, so it would be very difficult to do that. There's talk of even as many as 75,000 troops being needed to do this.
And finally, you could bomb these sites, but the danger there is if you don't do it properly, you could release a toxic cloud. But that option could be carried out, that bombing option, by either the U.S. or the Israelis if there's a sense the weapons might fall into the wrong hands, the hands of terrorists.
BLOCK: Tom, what is known about the extent of Syria's chemical weapons arsenal?
BOWMAN: Well, the sense is they have the largest chemical arsenal in the Middle East, hundreds of tons of chemical agents and hundreds, if not thousands, of artillery shells and missiles that could carry these chemical warheads. You know, what government officials worry most about is sarin. Now, this is the same kind of nerve agent that Saddam Hussein used in the 1980s to kill thousands of Kurdish men, women and children in northern Iraq.
Now, this is the main issue the Obama administration is focused on in Syria. They worry about these chemical weapons and in particular, the possibility they might fall into the hands of terrorists like al-Qaida.
BLOCK: NPR's Pentagon correspondent Tom Bowman, Tom, thanks very much.
BOWMAN: You're welcome. Transcript provided by NPR, Copyright National Public Radio.