KABUL — A roadside bomb in southern Afghanistan killed a U.S. service member, while an American civilian working for the military died after insurgents attacked a patrol in the east, officials said.

In Kabul, two mortar rounds were fired early Tuesday near the presidential palace in Kabul, the U.S. military said. U.S. spokeswoman Capt. Elizabeth Mathias had no details of damage or casualties from the attack, which occurred two days before presidential elections.

The military death Monday brought to 22 the number of U.S. troops killed in August, while foreign and Afghan forces step up their fight against the Taliban-led insurgency raging in much of the country's south and east.

A military statement would not disclose details on the latest casualties. It said only that the civilian died after insurgents attacked his patrol with gunfire.

Thousands of U.S. Marines are pushing ahead with their largest-ever operation in Afghanistan as they try to secure parts of southern Helmand province, a major Taliban stronghold.

A number of insurgent groups also operate in eastern Afghanistan, a mountainous area that borders Pakistan.

Attacks in Afghanistan have risen steadily the last three years. U.S., NATO and Afghan security forces are out in force this week to help protect voters taking part in Thursday's presidential election.

In a speech Monday in Phoenix, President Barack Obama spoke of fierce fighting against Taliban and other insurgents leading up to Thursday's Afghan national elections.

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He told a veterans' group that U.S. troops are working to secure polling places so that the elections can go forward and Afghans can choose their own future.

Obama said peace in Afghanistan "will not be quick" and "will not be easy."

He said the United States still has a deep interest in the long-term outcome.

"This is not only a war worth fighting. This is fundamental to the defense of our people," Obama said.

But a powerful Afghan insurgent leader said Afghans can decide their fate "without any trusteeship."

"America has to realize that it will not achieve victory in its war in Afghanistan through increasing the number of its soldiers in this country or through the sham elections," Gulbuddin Hekmatyar told the al-Jazeera news network in a Sunday evening interview.

Hekmatyar was a favored "freedom fighter" in the 1980s when the U.S. backed rebel groups trying to push the Soviet Union out of Afghanistan. Now his militants are committed to fighting international and U.S. troops in Afghanistan.

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Associated Press Writer Maamoun Youssef contributed to this report from Cairo.