Kabul, Afghanistan ? President Barack Obama paid a surprise visit to Afghanistan on Sunday as he sought to steel American forces for a tough summer fight and deliver a political jolt to Afghan President Hamid Karzai as he weighs potential peace talks with the Taliban.

In his first visit to Afghanistan since taking office, Obama firmly prodded Karzai to take more decisive steps to reform his corruption-tainted government so both leaders can capitalize on the surge of 30,000 more American troops into the war zone.

Speaking to nearly 2,000 military service personnel, at Bagram Air Field north of Kabul, Obama warned they faced “difficult days” in the escalating fight against Taliban insurgents.

Obama’s six-hour visit came at a pivotal moment for both the U.S.-led military coalition and the Karzai government.

After a successful military campaign in the opium-saturated Helmand Province, American forces are preparing for a more challenging showdown in Kandahar, the spiritual birthplace of the Taliban in southern Afghanistan.

The recent military offensive in Marjah helped shore up flagging public support in America for Obama’s strategy in Afghanistan. But support at home could waver as the fighting intensifies this summer.

At the same time, Karzai is preparing to hold a nationwide conference — a peace jirga — next month to discuss ways to end the eight-year-war by holding peace talks with pragmatic Taliban leaders.

Obama made no public mention of the potential peace talks, a contentious step that has not yet won broad support in Afghanistan or the U.S.

Some administration officials believe the U.S.-led military coalition needs to deliver a more decisive blow to the Taliban insurgency before entering any serious peace talks with their leaders.