US President Barack Obama wants Pakistan to step up its commitment to fighting Taliban militants who are growing in strength and compromising vital US interests. In meetings at the White House on Wednesday, Obama will press Pakistani President Asif Ali Zardari to do more against the Taliban, which recently has alarmed the US and its allies by striking out from strongholds on the Pakistani-Afghan border to areas closer to the capital of Islamabad. Obama also will seek renewed commitment from Afghan President Hamid Karzai to better coordinate operations with Pakistan and the US, which will expand its military presence in Afghanistan under the president's revised war strategy against the Taliban. Obama and his foreign policy and national security team were to meet separately and then together with Zardari and Karzai. The US team also will seek assurances from Zardari that his country's atomic weapons are secure. "The president is deeply concerned about the security situation," White House press secretary Robert Gibbs said Tuesday. "That's why we're sending additional troops to Afghanistan and that's why we'll talk with both the Afghans and the Pakistanis about our renewed commitment in helping them seek the aid that they need to address those extremists." Another issue arose early Wednesday, when Karzai ordered a probe into allegations by local officials that more than 30 civilians were killed in a bombing late Monday by US-led troops battling militants in western Afghanistan. The International Committee of the Red Cross said a team it had sent to the area saw "dozens of bodies in each of the two locations," including women and children. Karzai's office said he will raise the issue of civilian deaths with Obama. The US has sent a brigadier general to investigate. Senior administration officials say the goal of Obama's meetings with Karzai and Zardari is to get Afghanistan and Pakistan to work together against a shared extremist threat to their nations. They hope the message has huge weight coming straight from Obama. The results, they acknowledged, will be measured by whether the outreach leads to concrete actions. That includes, for example, the degree to which the Pakistani army shows a sustained commitment to fighting extremists within its borders. The officials spoke on condition of anonymity to discuss what will be private diplomatic exchanges. Officials say there is no movement by the Obama administration to send US military forces into Pakistan, a point on which Pakistani officials have been emphatic. "That's the end of that subject as far as we're concerned," one official said. Still, the administration will be seeking assurances that Pakistan's military intends to face down both Taliban and al-Qaida extremists in coordination with Afghanistan and the United States. On Tuesday, the administration's point man for the region told lawmakers, who are considering a major boost in US assistance to Pakistan - $1.5 billion a year over five years - that "our most vital national security interests are at stake" in Pakistan. Special envoy Richard Holbrooke insisted that Pakistan is not a "failed state," but is facing tremendous challenges that it acknowledges could affect the safety of the country's nuclear arsenal. Holbrooke said the US needs "to put the most heavy possible pressure on our friends in Pakistan to join us in the fight against the Taliban and its allies. We cannot succeed in Afghanistan without Pakistan's support and involvement." Holbrooke's comments came as Pakistan's military appeared ready to launch a new offensive against Taliban forces mobilized in the northwestern Swat Valley region. Black-turbaned militants roamed city streets and seized buildings as thousands of people fled the battleground. Pakistani officials braced for an exodus of half a million people. The fighting follows the collapse of a three-month truce with the Taliban in the valley that Secretary of State Hillary Rodham Clinton had likened to an abdication of government control to extremists. It will test the ability of Pakistan's military and the resolve of civilian leaders who had hoped the insurgents could be partners in peace. Obama and Clinton will hold two sets of meetings Wednesday with Zardari and Karzai, who made comments similar to Holbrooke's in a Tuesday speech at a Washington think tank. Karzai said the key to the Taliban's resurgence in recent years is its havens across the border in Pakistan. Holbrooke said the talks, which will continue at a lower level on Thursday, would be "historically important." "We are talking today about an issue that is of direct importance to our national security," he said, noting that comparisons of the situation to the Vietnam War were inaccurate because the enemy in that case had never posed a direct threat to the United States. The Taliban and al-Qaida remain the most serious threat to national security, he said. Ahead of Obama's discussions with Zardari and Karzai, Clinton will see them and their delegations separately at the State Department before bringing the two sides together. Later, at the White House, Obama will follow the same pattern in talks with the two leaders. On Thursday, other top Obama officials will meet separately with their counterparts from Afghanistan and Pakistan. Those include Agriculture Secretary Tom Vilsack, Attorney General Eric Holder and FBI Director Robert Mueller.