BAGHDAD, Iraq (CNN) -- Deaths among Iraqi civilians, security forces and insurgents jumped in March because of the recent spasm of violence in the country's Shiite regions, an Iraqi Interior Ministry official said.
An Iraqi woman grieves over the body of a Shiite militiaman during his funeral Monday in Najaf, Iraq.
"It's obvious that the [number of] killed and wounded have increased because of the military operation in Basra and the violence that erupted across the country after the operation started," the official said.
A government offensive that started last week in the southern city of Basra targeting "outlaws" resulted in tough fighting between troops and Shiite militants. Clashes spread to other southern cities and parts of Baghdad, leaving hundreds dead and wounded.
On Tuesday a U.S. airstrike targeted militia fighters in eastern Baghdad's Sadr City district, the heart of Shiite cleric Muqtada al-Sadr's support in the capital. The U.S. military did not release casualty figures from that attack, but denied reports from Iraqi authorities that civilians were killed in the strike.
Iraqi Prime Minister Nuri al-Maliki on Tuesday said the ongoing military operation in Basra is a "legitimate" effort that has been a success.
"We fulfilled our security commitments and responsibilities, which paved the way toward law enforcement and security," he said.
In March, 923 Iraqi civilians were killed in violence across the country and 1,358 were wounded, according to the Interior, Defense and Health ministries. The figure is sharply higher than February, when 633 civilians died and 701 were wounded.
Deaths among security forces spiked as well, with 54 soldiers killed and 100 wounded and 102 police killed and 173 wounded. In February, 20 soldiers were killed and 22 wounded, and 65 police were killed and 122 wounded.
The number of people the Iraqi government describes as "terrorists" who were killed and detained grew as well. There were 641 killed in March and 235 killed in February. There were 2,590 people listed as terrorists and terrorist suspects detained in March and 1,340 detained in February.
Last year, the civilian death tolls were much higher, as Sunni and Shiite sectarian violence and fighting between insurgents and troops raged. But the tolls began dropping in the summer.
There were 1,646 civilian deaths in February, 1,872 in March, 1,501 in April, 1,949 in May, 1,227 in June, 1,653 in July, 1,773 in August, 844 in September, 758 in October, 538 in November and 481 in December.
The successes of the U.S. military troop increase, a cease-fire by al-Sadr's Mehdi Army militia that began last summer and the growth of pro-U.S. Sunni groups called the Sons of Iraq and Awakening Councils had been among the reasons cited for the drop.
However, in light of last week's violence in Basra, Great Britain will keep its troop level at 4,000, British Defense Minister Des Browne said Tuesday.
British troops, which have been based in Basra, handed security control to Iraqi troops and police late last year. Britain had hoped to draw down troops to 2,500 by this spring if conditions permitted.
The U.N. refugee agency has increased its estimate of internally displaced people in the war-torn country to more than 2.8 million people, but it said the rate of new displacement is rising "at a much lower pace."
The information comes from a new report by a working group made up of U.N. agencies, nongovernmental organizations and Iraqi government agencies. This new displacement estimate shows an increase of about 300,000 from the last count, made at the end of 2007. The difference is largely due to the "improved entry" of information in the database of Iraq's Ministry of Displacement and Migration.
The displacement crisis in Iraq is the worst in the Middle East since the population changes in 1948 when the state of Israel was created, according to the U.N. High Commissioner for Refugees. Along with the internally displaced people, there are more than 2 million refugees, most of whom are in Syria and Jordan.
The violence that started last week in Basra highlighted the civil conflict among Iraqis. The offensive exacerbated the power struggles in Shiite regions across Iraq, pitting Iraqi security forces against Shiite militants, including al-Sadr's followers.
The warfare subsided after al-Sadr told his followers Sunday to lay down their arms, but the prevailing tension in the region threatens to unravel the government efforts to bring about stability in Iraq. Watch how Iran played a role »
Al-Sadr distributed a letter this week praising Mehdi Army members for their efforts during the fighting.
"Thank you for facing the difficulties, being patient, obedient, supportive of each other, defending your land, people and honor," said the letter -- signed by "your brother, Muqtada al-Sadr."
It was posted Monday on a Web site linked to the Sadrist movement.
"Peace be upon the mujahedeen [fighters] who did not leave a safe place for the enemies, and who consider the occupier as an enemy, and consider people as friends," al-Sadr wrote.
Al-Sadr said he appreciates their "efforts in facing the highest number of enemies. At the same time, I offer my condolences to the Iraqi martyrs and I ask God to heal the wounded."
In addition to the violence among Shiites, the U.S. military warns that al Qaeda in Iraq remains a major threat, and troops have been targeting the largely Sunni group in northern Iraq and Baghdad raids.
Meanwhile, the number of U.S. troop fatalities in March reached 38, a higher figure than in February but continuing the general decline in American troop deaths through the last six months.
Many of the U.S. troops killed were soldiers operating in the Baghdad area who were struck by roadside bombs, small-arms fire and indirect fire, according to military reports.
Other troops were killed in northern Iraq and Anbar province, west of Baghdad. The deadliest strike occurred in the capital on March 10, when a suicide attacker struck five U.S. soldiers on foot patrol.
Last year, 83 U.S. troops died in January and 81 in February and March each. The numbers grew to 104 in April, 126 in May and 101 in June. The figures dropped as reinforcements arrived, to 78 in July, 84 in August and 65 in September.
Since autumn the monthly numbers haven't risen above 40. There were 38 troop deaths in October, 37 in November, 23 in December, 40 in January, 29 in February and 38 in March.
Maj. Winfield Danielson noted several factors have played a role in the marked decrease in U.S. deaths since last year.
"The surge allowed us to go into terrorist safe havens, the [Iraqi security forces] are significantly more capable than they used to be, both in terms of their numbers and ability to work independently," he said. E-mail to a friend
CNN's Mohammed Tawfeeq and Jonathan Wald contributed this report.