President Bush urged Pakistani President Pervez Musharraf on Saturday to take new steps to rein in extremists who threaten to destabilize the U.S. coalition against terrorism. As tensions rose between Pakistan and India, Bush told Indian Prime Minister Atal Bihari Vajpayee the United States would cooperate with India in its fight against terror.

In a sign of the growing sense of urgency within the administration about the military buildup in the region, Bush called both leaders Saturday morning during his vacation here.

Bush expressed appreciation for Pakistan's "continued support" during the U.S.-led military campaign in neighboring Afghanistan, said White House spokesman Scott McClellan.

But Bush's message to Musharraf was much sharper than to Vajpayee.

Bush "urged President Musharraf to take additional strong and decisive measures to eliminate the extremists who seek to harm India, undermine Pakistan, provoke a war between India and Pakistan and destabilize the international coalition against terrorism," McClellan said.

He would not elaborate on what steps Bush sought, or what it meant to "eliminate" the extremists.

The crisis in the region flared after a Dec. 13 attack by gunmen on India's Parliament that India blamed on Pakistan-based militants backed by the Pakistani government. Pakistan denies involvement in the attack, which left nine Indians and the five attackers dead.

Bush told Vajpayee the United States is "determined to cooperate with India in the fight against terrorism," and reiterated his outrage over the attack, calling it "a strike against democracy."

He urged both leaders to work to reduce tensions, McClellan said.

The president also discussed the crisis with British Prime Minister Tony Blair, who plans to travel to the region in the coming days, McClellan said.

Bush has used personal calls to world leaders sparingly in times of crisis. His conversations Saturday were the first with Vajpayee since Dec. 13 and with Musharraf since the two met in New York on Nov 10.

Further reinforcing a growing sense of urgency, Secretary of State Colin Powell spent Saturday again discussing the situation with Musharraf and Indian Foreign Minister Jaswant Singh, a State Department official said. Powell also spoke with the two leaders on Friday.

McClellan would not comment on a report Saturday in The Washington Post that the administration feared an Indian military strike against Pakistan.

"India and Pakistan are areas of continued concern, and the president thought it was important to speak to both leaders," McClellan said.

India and Pakistan have said repeatedly they want to want to avoid war. But Bush's discussions with the leaders came as both seemed to be drawing closer to military conflict.

Indian and Pakistani soldiers — only 100 yards apart in some places — traded fire again Saturday over the "Line of Control" dividing the disputed Kashmir region, as civilians on both sides of the border were evacuated.

India said Saturday it would continue to mass tens of thousands of troops at its border until Pakistan cracks down on Islamic militants, rejecting a Pakistani call for the two nations' leaders to meet to try to defuse the crisis.

Pakistan warned that the tensions could trigger a full-fledged conflict between the nuclear-armed nations.

On another crisis front, Bush also spoke with Argentine President Adolfo Rodriguez Saa about that country's financial crisis. He signaled the United States' willingness to back Argentina through the International Monetary Fund and other institutions if the Argentine government puts a sustainable economic plan in place.