Democratic presidential contender Barack Obama arrived in Afghanistan, at the beginning of a Europe and Mideast trip aimed at helping him bolster his foreign policy and national security credentials, an area in which Republicans say his experience is inadequate for the White House. The Illinois senator arrived Saturday in Kabul as part of an official congressional delegation and then flew to eastern Afghanistan. Staff. Sgt. David Hopkins said Obama and two other senators were making a brief stop in Jalalabad airfield, in Nangarhar province, to visit with soldiers stationed there. The delegation also met with top military leaders and troops at Bagram Air Base, the main US military base in the country, according to a US military officer who spoke on condition of anonymity because the officer was not authorized to release the information. Obama's first visit to Afghanistan, coming less than four months before the general election, was rich with political implications. Republican presidential rival John McCain has criticized Obama for his lack of time in the region. Obama is also expected to stop later in Iraq. "I look forward to seeing what the situation on the ground is," Obama told a pair of reporters who accompanied him to his departure from Andrews Air Force Base on Thursday. "I want to, obviously, talk to the commanders and get a sense both in Afghanistan and in Baghdad of, you know, what the most, their biggest concerns are, and I want to thank our troops for the heroic work that they've been doing." Sultan Ahmad Baheen, spokesman for Afghanistan's Foreign Ministry, said Saturday that Obama would meet with President Hamid Karzai during his visit. Underscoring the challenges in Afghanistan, authorities reported Saturday that a roadside bomb killed four policemen in the volatile south of the country where the Taliban-led insurgency is intensifying nearly seven years after a US-led invasion ousted the militant movement from power. In an interview with The Associated Press conducted in Baghdad Saturday, the top American commander in Iraq, Gen. David Petraeus, said senior leaders of al-Qaida may be diverting fighters from the war in Iraq to the Afghan frontier area. Petraeus also said al-Qaida may be reconsidering Iraq as its highest priority war front. En route to Afghanistan, Obama stopped Friday at Camp Arifjan, the main US military base in Kuwait and a major gateway for US soldiers moving into and out of Iraq. Lt. Col. Bill Nutter, a spokesman for the US military in Kuwait, said, "He talked to soldiers and constituents and met with senior military leadership." During the two-hour visit, Nutter said, the officers gave him an overview of operations. Obama shook hands, answered questions, posed for photos and played a little basketball during the visit. Obama has pledged to withdraw combat troops from Iraq within 16 months if he is elected, and argues that McCain offers nothing more than an extension of Bush's unpopular policies. He has maintained that McCain would do little more than continue a war that has diverted necessary US forces from the conflict in Afghanistan where Taliban and al-Qaida militants are regrouping, posing a renewed risk to Americans. The Democrat, who is seeking to become the first black US president, has spent much of the week outlining his foreign policy views, even as the faltering US economy has eclipsed Iraq as the top campaign issue in the November election. McCain, a former Navy pilot and Vietnam prisoner of war, has trumpeted his foreign policy credentials while trying to focus his campaign on the country's economic struggles. The presumptive Republican nominee's attempts to appeal to voters concerned about their livelihoods and rising prices were tarnished a week ago when one of his top advisers, former US Senator Phil Gramm, said the United States had become a "nation of whiners" who constantly complain about the economy. Gramm Friday resigned from McCain's campaign and said in a statement he wanted to "end this distraction." Earlier in the day, in an appearance before General Motors workers in Michigan, McCain once again sought to counter the impression that he was not as strong as Obama on the economy. He promised the auto workers that he would help make the company's long-range electric car a success as he outlined ways to help a state and industry hit hard by the economy. Also Friday, the veteran Arizona senator aired a new TV ad saying that while Obama has not been to Iraq for years, and voted against war funding to win the Democratic nomination, he is now "changing to help himself become president." McCain, it says, has always supported the Iraq strategy "that's working" _ a reference to the troop buildup credited for sharply reducing violence in the country. Obama's trip affords the first-term senator _ who currently leads McCain in many polls but is, at best, tied on those relating to foreign policy _ a chance to promote his plans to mend rifts with allies weary of the Bush administration and end the Iraq war. Campaign officials have announced stops in Jordan, Israel, Germany, France and Britain. The visits could also factor in his favor in further invigorating supporters and winning over others like independents and swing voters. An Associated Press-Yahoo News poll showed that Obama's supporters are much more energized by the election than McCain's are. It showed that 38 percent of Obama's supporters say the election is exciting compared with 9 percent of McCain's. The passion and interest shown by blocs of voters are important because they affect who will be motivated to vote.