BAGHDAD — Violence appeared to be on the rise in Iraq after a day that saw at least 42 people die — numbers that cast doubt on the easing of sectarian violence following a surge of American forces to the country last year.

An Iraqi official confirmed the grisliest attack yesterday when 16 passengers on a bus in southern Iraq were killed by a roadside bomb. The American military, however, claimed no one died in the attack, which was targeting a passing military convoy. The reason for the discrepancy was not immediately clear.

The head of the Nasiriyah provincial health directorate, Dr. Hadi Badr al-Riyahi, confirmed today that the attack on the bus traveling from Najaf to Basra killed 16 civilians and wounded 20.

At the time, a local policeman and the assistant bus driver also said 16 people were killed.

But a military spokesman in Baghdad, Major Brad Leighton, disputed that claim today, saying that only one coalition soldier and one Iraqi civilian were wounded in the attack about 50 miles from Nasiriyah, about 200 miles southeast of Baghdad.

At least 26 people were killed yesterday in other violence around the country.

The spike comes in the wake of a 60% drop in attacks across the country since June, according to American military figures.

According to an Associated Press count, at the height of unrest between November 2006 and August 2007, on average approximately 65 Iraqis died each day as a result of violence. As conditions improved, the daily death toll steadily declined. It reached its lowest point in more than two years in January, when on average 20 Iraqis died each day.

Those numbers have since jumped. In February, approximately 26 Iraqis died each day as a result of violence, and so far in March, that number is up to 39 daily. These figures reflect the months in which people were found, and not necessarily — as in the case of mass graves — the months in which they were killed.

Last Thursday, two massive bombs killed 68 people in Baghdad’s Karradah neighborhood, while on March 3, two car bombs killed 24 people in the capital.

A military spokesman, Rear Admiral Gregory Smith, said Sunday that recent violence should not be taken as evidence of “an increase or a trend of an increase.”

“I think we need to continue to look at historically what has happened over the last year to really put in perspective a one-week or two-weeks’ worth of activity inside Baghdad,” Admiral Smith said.

An American soldier died yesterday after his patrol was hit by a roadside bomb near Diwaniyah, 80 miles south of Baghdad, a day after eight soldiers died in a pair of bomb attacks marking the heaviest single day of American casualties since September.

Today, two Iraqi civilians were killed and 10 others wounded when a roadside bomb exploded near a passing American military patrol, local police said. There were no reports of American casualties.