Violence in Iraq is at its lowest levels since the first year of the American invasion, finally opening a window for reconciliation among rival sects, the second-ranking US general said as Iraqi forces formally took control of security across half the country. Lt. Gen. Ray Odierno, the man responsible for the ground campaign in Iraq, said Sunday that the first six months of 2007 were probably the most violent period since the US-led invasion in 2003. The past six months, however, had seen some of the lowest levels of violence since the conflict began, Odierno said, attributing the change to an increase in both American troops and better-trained Iraqi forces. "I feel we are back in '03 and early '04. Frankly I was here then, and the environment is about the same in terms of security in my opinion," he said. "What is different from then is that the Iraqi security forces are significantly more mature." British forces on Sunday formally handed over responsibility for Basra, the last region in Iraq under their control. The transition marked the start of what Britain hopes will be a transition to a mission aimed at aiding the economy and providing jobs in an oil-rich region beset by militia infighting. Meanwhile, violence killed at least 27 Iraqis on Sunday - 16 of them members of a US-backed neighborhood patrol killed in clashes with al-Qaida in a volatile province neighboring Baghdad. Thirty-five al-Qaida fighters also died in that fighting, Iraqi officials said. Odierno said Anbar province, once plagued by violence, only recorded 12 attacks in the past week, down from an average of 26 per week over the past three months. "The violence last week was the lowest ever," he said of Anbar. "So that kind of defines 2007 very simply. A long hard fight and a lot of sacrifice by a lot of soldiers, Marines and airmen to get there," Odierno said. A planned reduction of troops to about 130,000 at the end of next year from a high of around 165,000 at the height of the "surge" should not derail that effort, but Iraq's government must take advantage of the improved security, Odierno said. There are 154,000 US troops in Iraq now. "We have a window, I don't know how long that window is, but there is a window because of the security to move forward," Odierno told a small group of journalists at his headquarters in Baghdad. "We need to get policies in place by the central government to do this." One of the most important, he said, was a draft bill to ease curbs implemented against former supporters of Saddam Hussein's Baath Party in the aftermath of the 2003 invasion. Iraqi lawmakers are debating the US-backed draft law that would pave the way for the creation of a National Commission for Accountability and Justice, an independent body that would screen former Baath members in place of the de-Baathfication commission, which many Sunnis have complained has been overly zealous in purging low-ranking party members who had in many cases joined the party under pressure from Saddam and been following orders. "Reconciliation must continue," Odierno said. The US-led coalition has been gradually transferring control of security to the Iraqi government and Britain's handover of southern Basra was the latest in a series that began in July 2006. The coalition retains control over half of Iraq's 18 provinces, including Anbar and central areas where violence has waned but not stopped. "This is a step toward resuming security responsibilities in all of Iraq's provinces that is due in the middle of next year," Iraqi National Security adviser Mouwaffak al-Rubaie said in Basra. He represented Prime Minister Nouri al-Maliki at the handover ceremony in the capital of the oil-rich region. US Secretary of State Condoleezza Rice, en route to Paris for a gathering of world donors to the Palestinians, said she was "heartened" by Britain's handover of Basra. "We obviously recognize and the British recognize that there's still a lot of work to do in terms of building a stable foundation in the south and there continue to be problems there," Rice told reporters on the flight to Paris. "We're very heartened that there's a sense that security can be turned over. But it doesn't mean that there aren't continuing problems in the south." In Diyala, one of Iraq's most dangerous regions, al-Qaida militants tried to regain control of several villages around Khalis, 50 miles (80 kilometers) north of Baghdad, but the US-backed volunteers drove them away, said Abdul Karim al-Rubaie of the provincial command center. Sunnis have been turning against al-Qaida in significant numbers and signing up for the volunteer security forces - partly in disgust at the militant group's brutal tactics, and partly to seek American protection against what they see as government-backed Shiite militias. "It is a battle of life and death, it is a continuous fight until we cleanse all the villages on the outskirts of Khalis," said Sheik Zuhair al-Obeidi, who was involved in Sunday's fighting. Al-Qaida's No. 2 Ayman al-Zawahri warned of "traitors" among insurgents in Iraq and called on Iraqi Sunni Arab tribes to purge those who help the Americans in a new videotape posted Monday on the Web. Al-Zawahri's comments were aimed at undermining so-called "awakening councils" - the groups of Iraqi Sunni tribesmen that the US military has backed to help fight al-Qaida in Iraq and its allies. Next summer is more than half a year longer than President George W. Bush's prediction in January that Iraq would assume control all of its provinces by November. Giving responsibility to the Iraqi army and police does not necessarily mean that violence will abate in Basra, where rival Shiite parties and militias have fought for control of the province. "This remains a violent society whose tensions need to addressed, but they need to be addressed by Iraqi political leaders," British Foreign Secretary David Miliband, who also attended the handover ceremony, told the British Broadcasting Corp. Gen. David Petraeus, the top American commander in Iraq, said in a joint statement with US Embassy Deputy Chief of Mission Patricia A. Butenis, that Iraqi forces "have demonstrated their readiness to assume responsibility for the provincial security. Today this responsibility is theirs." British troops will not immediately leave southern Iraq but will instead remain at their base just outside the city. This is know by the military as "operational overwatch," in which Iraqi security forces and civilian police take responsibility under a provincial governor, or other official, and coalition forces are held in reserve in bases that are spread out - intervening when necessary or when asked. The next phase would involve a hand over at a national level - which could then set stage for a large-scale withdrawal of all foreign troops a few years later.