Kabul ? A suicide bomber struck a U.S. convoy in southern Afghanistan on Friday, killing two American soldiers, and military officials announced the deaths of two other international troopers — one American and one Briton — the day before.

The deadly start to the month followed a drop in U.S. and NATO deaths in September over the previous two months — perhaps because no major offensives were launched as the U.S. takes stock of its strategy in the troubled eight-year war. The Obama administration is debating whether to send more American troops to Afghanistan.

President Barack Obama summoned his top commander in Afghanistan, Gen. Stanley McChrystal, for a 25-minute meeting aboard Air Force One on Friday in Copenhagen, Denmark, as part of his review of a war strategy that has divided the president’s national security team.

The two conferred just before the president returned to Washington from Copenhagen, where he made a pitch to the International Olympic Committee on behalf of Chicago’s unsuccessful bid to host the 2016 games.

U.S. spokeswoman Capt. Elizabeth Mathias confirmed the deaths in Friday’s convoy attack but would not specify where they occurred. Afghan police reported a suicide attack west of Kandahar but were uncertain if there were U.S. casualties.

Mathias also said a third American died late Thursday after militants fired rocket-propelled grenades at a patrol in eastern Afghanistan. Several other Americans were wounded, she added.

In London, the British Ministry of Defense announced that a British airman was killed Thursday when a bomb exploded alongside his patrol near Camp Bastion in southern Helmand province, one of the flashpoints of recent fighting.

The four deaths were the first reported this month for the U.S.-led international force, which has been locked in the heaviest combat of the Afghan war.

Nevertheless, the number of American troops killed in the war dropped from a record monthly high of 51 in August to 37 in September, according to figures compiled by The Associated Press from official statements.

U.S. death tolls had been rising steadily since the spring following Obama’s decision to send 21,000 more troops to Afghanistan to curb the growing Taliban-led insurgency. American deaths went from 12 in May to 24 in June and 44 in July.

The September death toll for the overall international force, including Americans, stood at 65, compared with 73 in August.

At the same time, however, Afghan civilian deaths rose from 169 in August to 202 in September, according to AP figures compiled from police and other Afghan officials. The increase may have been a result of stepped-up Taliban attacks on civilian traffic along major highways, including a bomb blast Tuesday that killed 30 bus passengers west of Kandahar.

U.S. spokesmen declined to speculate on what may have been responsible for the decline in American deaths last month and whether it marked the start of a trend.

The reason could simply be that no large-scale ground offensives were launched against the Taliban and their allies in September.

U.S. forces mounted major operations in July and August in southern Afghanistan to try to dislodge the Taliban from longtime strongholds and improve security ahead of the Aug. 20 presidential election, the outcome of which remains in doubt because of allegations of massive fraud by supporters of President Hamid Karzai.

Those allegations as well as rising combat losses have triggered a debate within the U.S. administration and Congress over the future of the U.S. mission, which began in 2001 when a U.S.-led force drove the Taliban from power after their refused to hand over al-Qaida boss Osama bin Laden.

McChrystal is widely believed to want to add between 30,000 and 40,000 troops to the current U.S. force of 68,000. Other senior officials, including Vice President Joe Biden, favor a strategy that directly targets al-Qaida fighters believed to be hiding in Pakistan rather than significantly increasing troop levels in Iraq.

No decisions were announced after McChrystal’s meeting with the president, but White House press secretary Robert Gibbs told reporters that the two agreed that a review of war strategy “is a helpful process.”