(CNN) -- British troops Sunday handed over responsibility for security in the southern Iraqi province of Basra, a major milestone in the scaling-back of the foreign military presence nearly five years after the U.S.-led invasion.
Soldiers hang a large Iraqi flag in Basra in preparation for the handover ceremony.
"As you step up, we step back," the British commander, Maj. Gen. Graham Binns, told Iraqi troops and political officials, at a transfer ceremony broadcast live on Iraqi state television.
The changing of the guard came on the same day that Iraq resumed train service from Basra to Baghdad after a four-year hiatus.
The handover of Basra became official with the signing of a "memorandum of understanding" by Iraqi and British officials.
Britain has been in command of the south since the Iraq War began, with its troops based in Basra. It has been working to withdraw its troops from the region, which has always been more stable than Baghdad and other outlying regions.
Roughly 5,000 British troops are there now. Prime Minister Gordon Brown's government has announced plans to cut forces to about 4,500 by the end of December.
National Security Adviser Mowaffak al-Rubaie said the transfer means that Basra police will be the first called to respond to any security incident, and will be backed up by the Iraqi Army as needed.
British troops could be called in to help, but it would be coordinated through the office of Prime Minister Nuri al-Maliki in Baghdad, he said.
"Our help will continue to be one of assistance, not interference, to support not to direct, to listen not to ignore, to understand not to fear," Binns said. Watch Binns deliver address at ceremony »
Improved security allowed Basra to begin its long-stalled train service to the capital, said Gate'e al-Mayahi, chief of Baghdad's central railway station.
The train route runs between the towns of Latifiya, Mahmoudiya and Yusufiya, Iraq's "triangle of death." The trains stopped running four years ago because of insurgent attacks.
Railroad officials, spectators and journalists gathered at the Allawi station Sunday morning for a ribbon-cutting ceremony. Traditional music filled the air as people waved the V-for-victory sign. Several men boarded the train about 9 a.m. as Iraqi police looked on.
The train stops at stations in Hilla, Diwaniya, Samawa and Nasiriya. Al-Mayahi said plans are under way to resume train service to the northern city of Mosul once the tracks are fixed.
"This is proof that the security situation has improved," he said.
The British military, which is now emphasizing the training of local troops and police, plans to reduce its troop deployment to 2,500 by spring.
"There are now 30,000 Iraqi police and armed forces in the region," the Defense Ministry said in a statement on its Web site last week.
Brown, during a visit to Iraq last week, recommended that Basra province, not just the city of Basra, be returned to Iraqi security control during December.
Maj. Gen. Binns said last summer he did not expect they would be ready for a handover by the end of 2007.
"There has been an extraordinary and dramatic reduction in the level of violence in last few months, and the people who can take credit for this are the Iraqi security forces," Binns said. Watch as British troops prepare to hand over »
Al-Rubaie said "huge progress" has been made in "cleaning a lot of bad elements in the police," but it remains a "huge challenge" and "one of the main tasks."
British Foreign Secretary David Miliband and British Ambassador to Iraq Christopher Prentice also attended the Basra ceremony, which was held at the British headquarters at the airport outside of Basra. E-mail to a friend
CNN's Jomana Karadsheh contributed to this report.
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