At least 20 people have been killed in an attack on a security compound and government building in the flashpoint town of Falluja, west of Baghdad. Fourteen police officers and three gunmen were reported among the dead. Many prisoners were freed from a holding centre. It is not known why they were being detained. The gunmen also attacked the local mayor's office, about a kilometre away, police said. The attack came two days after the top US commander in the Middle East, Gen John Abizaid, escaped injury in an attack by insurgents in Falluja. Up to 50 men took part in the latest raid which also left about 30 people injured, it was reported from the town. "Unknown men fired mortars, explosives and light machine guns from four directions. Their weapons were more powerful than our Kalashnikovs," police officer Earazan Abu Issa told Reuters news agency. US troops have moved in to the secure the area. The town lies in an area known as the so-called Sunni Triangle, the heartland of the guerrilla campaign against the US-led occupation of Iraq. As the violence continues, diplomatic efforts are under way to establish a stable political order in the country. But a UN official sided with the United States in its dispute with Iraq's top Shiite clergy over elections, saying Friday it would be hard to organize a vote before the June 30 deadline to hand power to the Iraqis. The United Nations' special envoy to Iraq said major changes will be needed in the US formula for creating the next Iraqi government. The envoy, Lakhdar Brahimi, also warned Iraqis to be wary of the risks of civil war as they compete for power. Brahimi met with council members Friday as he ended a weeklong mission requested by Washington after its plans came under criticism from Iraq's most influential cleric, Grand Ayatollah Ali al-Husseini al-Sistani. A spokesman for Brahimi said al-Sistani's demand for nationwide balloting would probably be too difficult to pull off by July. "The time between now and June is very short and that makes it unlikely that you can put mechanisms in place," UN spokesman Ahmad Fawzi told The Associated Press. "The elections don't have to happen before then." Brahimi told reporters the Iraqi people's demand for elections was legitimate but Iraqis "should know that elections is a complicated process" and "holding reasonably credible elections is also extremely important." **PHOTO CAPTION*** Al-Akhdar al-Ibrahimi (L) is in Iraq to discuss early elections.