A roadside bomb exploded in the Afghan capital Tuesday, killing two Afghans riding in a taxi, as fighting in eastern provinces left a U.S. soldier and seven suspected Taliban dead, officials said.

Also, the Afghan government appealed for $76.4 million to tackle an "imminent food crisis" caused by prolonged drought, particularly in the north and northwest.

The bomb on a busy Kabul road — the latest in a series of blasts that have rattled the capital — killed a man and woman in the taxi and wounded four other people, police official Faiz Ahmad Hotaq said.

CountryWatch: Afghanistan

In eastern Kunar province, an American soldier was killed Monday in a firefight with militants, coalition spokesman Col. Tom Collins said.

At least 258 members of the U.S. military have died in Afghanistan, Pakistan and Uzbekistan as a result of the U.S. invasion of Afghanistan in late 2001, according to the Defense Department.

Seven militants also were killed Monday in Paktika province in clashes with coalition soldiers, he said. One coalition soldier was slightly wounded.

Violence has escalated sharply in Afghanistan this year, as Taliban-led rebels have stepped up attacks, particularly in their former southern heartland. The deadliest spate of Taliban violence since the hard-line regime's 2001 ouster for harboring Usama bin Laden has drawn a tough response from Afghan and foreign forces.

More than 600 suspected Taliban militants have been killed since the June 10 launch of Operation Mountain Thrust, a U.S.-led offensive to crush the resurgent Taliban in southern Afghanistan, a coalition spokesman said Tuesday.

At least 19 coalition soldiers have been killed in the south during the same period, according to an Associated Press count based on coalition information.

NATO-led forces are preparing to take over command of security operations in former Taliban strongholds across the south, a move that could lead to a reduction in the more than 21,000 U.S. troops in Afghanistan.

NATO is increasing its troop numbers in Afghanistan from 9,700 to 16,000 in one of the biggest and most dangerous missions in alliance history. The surging violence has raised new concerns about the future of the war-battered country's fledgling democracy.

President Hamid Karzai condemned the fatal shooting of an Afghan doctor and a driver for the international Christian aid organization World Vision. The pair were killed Sunday after they delivered medicines to the town of Charsada in Ghor province — a rare attack in a relatively stable region.

A statement by Karzai said the two were killed "at the instructions of foreigners," but it did not elaborate.

Afghan officials often accuse neighbor Pakistan of providing haven for Taliban-led guerrillas. Pakistan has denied the allegations, saying it does all it can to prevent cross-border infiltration by militants.

Also Tuesday, the Afghan government and United Nations launched an emergency appeal to help the country through a shortfall in this year's wheat harvest due to the prolonged drought.

The money would support the "urgent needs" of more than 2.5 million people for six months, a joint statement by the Afghan government and the United Nations said.

Agriculture accounts for 52 percent of the impoverished nation's gross domestic product.

In other violence, the U.S. military said Tuesday that two American engineer soldiers were seriously wounded in a roadside bomb attack in eastern Khost province.

The two were on their way to a road project Sunday between the towns of Khost and Gardez when they were attacked, the military said. Their wounds were serious but not life threatening.