The Bush administration escalated sharp diplomatic warnings to Syria today, accusing Iraq's neighbor of developing chemical weapons, harboring former Iraqi leaders and allowing foreign fighters to enter Iraq to attack U.S. troops.

White House press secretary Ari Fleischer, at his morning briefing, said repeatedly that "Syria needs to cooperate." He read from a CIA report to Congress last year that Syria had stockpiles of the nerve agent sarin, that it was "trying to develop more toxic and persistent nerve elements," and that it was "highly probable" that Syria was pursuing biological weapons. Fleischer described the document as "authoritative" and said the charge is "well corroborated."

Fleischer declined to dispel the impression that administration was targeting Syria for possible diplomatic or even military measures. "I can only say to you that it should not be unexpected that the United States for a considerable period of time has said through diplomatic channels that nations that are rogue nations need to clean up their act," he said. "They should not harbor terrorists. They should not produce weapons of mass destruction."

Syrian officials denied Washington's charges, calling the increasing administration rhetoric a "campaign of misinformation and disinformation." Imad Moustapha, deputy ambassador to the United States, told the Reuters news agency that the administration's statements were meant to distract from the "human catastrophes" taking place in Iraq.

At the Pentagon, Defense Secretary Donald H. Rumsfeld told reporters that Syria had allowed "some Iraqi people" to cross its borders, "in some cases to stay and some cases to transit." Foreign fighters were also allowed to enter Iraq via Syria to target U.S. troops, Rumsfeld said after talks with Kuwait Minister of State for Foreign Affairs Sheikh Mohammad al-Salem al-Sabah. Rumsfeld also said Syria had tested chemical weapons.

Secretary of State Colin L. Powell, speaking to reporters after his own meeting with the Kuwaiti foreign minister earlier in the day, said the United States will examine possible diplomatic or economic measures against Syria.

"With respect to Syria, of course we will examine possible measures of a diplomatic, economic or other nature as we move forward," Powell said.

"In light of this new environment they [Syria] should review their actions and their behavior, not only with respect to who gets haven in Syria and weapons of mass destruction but especially the support of terrorist activity," Powell added.

Today's focus on Syria came after President Bush, for the first time, personally accused Syria of developing chemical weapons. "I think that we believe there are chemical weapons in Syria," Bush said yesterday. U.S. officials said yesterday they took Bush's statement as very significant, since the possession of weapons of mass destruction was the president's chief reason for confronting Iraq.

Bush also said Syria "needs to cooperate with the United States and our coalition partners and not harbor any Baathists, any military officials, any people who need to be held to account for their tenure during what we are learning more and more about."

In Iraq yesterday, U.S. and British officials said that a half-brother of Saddam Hussein, Watban Ibrahim Hasan, had been captured in Iraq trying to flee to Syria and was in U.S. custody.

At his afternoon news briefing, Fleischer said the administration hoped the ousting of Hussein's government would make an impression on Syria and other countries on the State Department's list of nations that support terrorism. "I think when you take a look at why nations find themselves on the State Department list of terrorist states, it's because they made bad choices and bad decisions," Fleischer said, echoing remarks the spokesman frequently made about Hussein's "bad choices" before the war in Iraq began. "And what the president is hopeful of is that in the outcome of this war, nations will examine the decisions they have previously made and, hopefully, make new decisions based on new reality in the Middle East. Gone is the brutal dictatorship of Saddam Hussein."

Fleischer said the administration hoped Syria and other nations would reexamine "how they conduct their affairs and how diplomacy is conducted, and whether or not they believe they should continue to be terrorist states or not. And a early indication of Syria's actions will be whether or not they harbor these Iraqi leaders."

Pressed by White House reporters earlier in the day on whether the administration was sending the message that it was threatening an invasion of Syria, Fleischer said, "People have to realize there are acceptable standards of behavior that world and certainly the free Iraqi people hope will be followed by its neighbors, including Syria, and part of that is not to harbor Iraqi leaders. Syria needs to cooperate and not harbor Iraqi leaders."

Fleischer made clear there was no commitment to hostilities with Syria. "Every nation will be treated as events warrant," he said. "Not every solution applies equally around the world." But Fleischer said that "Syria is indeed a rogue nation" and suggested it must rid itself of Hezbollah, a terrorist group that is a principal foe of Israel.

"Nations that are interested in peaceful outcomes to world affairs -- and do not interpret this as saying the United States has made a decision of action -- when you talk about making peace in the Middle East, broadly speaking, nations should not pursue polices that ferment or encourage or harbor terrorism," Fleischer said.

Asked why the increasingly hostile rhetoric was being directed at Syria at a time when world jitters had just begun to calm, Fleischer demanded: "Do you think the White House and President Bush should look the other way at the fact that Syria is taking in Iraqi leaders?" As for why the White House decided to raise the issue of the months-old CIA report on chemical weapons in Syria, Fleischer said "it's a relevant fact."

Syria denied the Bush administration's charges about chemical weapons. "We say to him [Bush] that Syria has no chemical weapons and that the only chemical, biological and nuclear weapons in the region are in Israel, which is threatening its neighbors and occupying their land," Foreign Ministry spokeswoman Buthaina Shaaban told Reuters today.

Shaaban also denied that Syria had cooperated with the government of Saddam Hussein. "There was never any cooperation between Damascus and Baghdad, our support was for the Iraqi people who have suffered the plights of wars," he said.

In Bahrain, British Foreign Secretary Jack Straw emphasized that Washington and London have no plans to invade Syria, but said Damascus had "important questions" to answer about its weapons programs. "As far as 'Syria next on the list,' we made clear that it is not," Straw said.

"There is no 'next' list," he said. "There are important questions which the Syrians need to answer."

Syrian President Bashar Assad met today with British Junior Foreign Minister Mike O'Brien, who came to Damascus as part of a tour that would also take him to Iraq. A British Embassy official told Reuters that O'Brien's visit was "part of ongoing dialogue between Syria and Britain." Assad also met today with Saudi Foreign Minister Prince Saud.