Iraqi forces are successfully filling the security vacuum as US combat troops withdraw from Iraqi cities ahead of a June 30 deadline, Iraq's UN envoy said Thursday. Ambassador Hamid al-Bayati said Iraq has already taken responsibility for 90 of the 138 military sites where US troops were in charge of security, and by the end of the month the ministries of defense and interior will be responsible for the remaining 48 sites. The withdrawal from the cities will be a major test for Iraq's army and police, which failed to stem a wave of Shi'ite-Sunni slaughter in 2006. That prompted the US troop surge of 2007 which is widely credited with quelling the violence. Many Iraqis are happy to see foreign soldiers off their streets but fear their own security forces may not be up to the challenge. US troops are moving to bases on the edge of cities by June 30 in case the Iraqis call for help. But under the US-Iraqi security pact reached last year, all US troops will leave the country by the end of 2011 - including the roughly 50,000 who will be left behind after the combat troops withdraw next year. "The process of building Iraqi defense capabilities to fill the security vacuum created with the withdrawal of friendly forces continues successfully," al-Bayati assured the UN Security Council. He said the security situation continues to improve, noting that between March and May the number of violent acts decreased by 76 percent compared to the same period in 2008. The improvement confirms "the development of security forces' capability and the significant decline in the capabilities of terrorist groups," al-Bayati said.