From his remote Texas ranch, President George W. Bush reached across the world as he tried to defuse worsening India-Pakistan tensions that threatened to flare into a regional nuclear war. 

India said Saturday it would keep massing troops, now numbering in the tens of thousands, at the Pakistani border until Islamabad cracks down on Islamic militants. New Delhi rejected a Pakistani suggestion that the two nations' leaders meet before things got worse. 

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. 

In telephone calls Saturday morning to Pakistani President Pervez Musharraf and Indian Prime Minister Atal Bihari Vajpayee, Bush used very different stances to try to settle things. 

Bush warned Musharraf, a general who peaceably seized power from a weak civilian government, to go further in controlling "extremists" who have been linked to the deadly suicide attack on India's Parliament on Dec. 13 which left 14 dead. 

The American president said he feared the conflict could unravel the U.S.-led coalition against terrorism based in Afghanistan, in which Pakistan has played a major role at considerable risk of its own destabilization by Islamic extremists. 

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," White House spokesman Scott McClellan said. 

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

Pakistan has reportedly already begun to shift troops strength from the Afghan to the Indian border, weakening the effort to prevent fleeing Taliban or Al Qaeda members, including suspected terrorist Usama bin Laden, from slipping into the loosely administered Tribal Areas of Pakistan. 

Pakistani Foreign Minister Abdul Sattar denied in an interview with CNN Saturday that Pakistan had moved any troops away from the Afghan border. 

In contrast to the tone he used with Musharraf, Bush was almost congenial with Indian Prime Minister Vajpayee, with whom, he assured, the United States would cooperate in the global fight against terrorism. He added that the parliament attack was "a strike against democracy." 

Bush urged both Musharraf and Vajpayee to exercise restraint, McClellan said. 

Further reinforcing the heightened sense of emergency, Secretary of State Colin Powell spent a second straight day discussing the situation with Musharraf and Indian Foreign Minister Jaswant Singh, a State Department official said. Powell had also spoken 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. 

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

Sattar said on CNN that he welcomed Bush's words, saying that "the United States, as the leader, the leading power of the world, can exercise salutary influence." 

Bush has used personal calls to world leaders sparingly in times of international 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. 

He placed the calls a day after saying his administration is "working actively to bring some calm in the region, to hopefully convince both sides to stop the escalation of force." 

On another international front, Bush 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. 

The Associated Press contributed to this report.