Kabul , Afghanistan ( CNN ) -- New U.S. commander Gen. David Petraeus arrived in Afghanistan Friday , a day marred by violence in a part of the troubled nation that was relatively peaceful a year ago . Petraeus arrived at NATO headquarters in Kabul in the evening , the International Security Assistance Force said . Earlier in the day , Taliban militants in the northern city of Kunduz attacked the compound of a U.S. aid agency subcontractor , killing at least five people and wounding 20 others , government officials said . On the day of Petraeus ' arrival , the brazen attack served as a grim reminder for international forces that they face a difficult challenge in overcoming the Taliban insurgency , which many say has been gaining momentum . A year ago , places like Kunduz were regarded as safe -- but not anymore . The pre-dawn raid started when a suicide bomber on foot and another in a car detonated at the gate of the compound , said Mohammad Omar , the provincial governor . Following the initial assault , four gunmen stormed the facility , firing machine guns and throwing hand grenades , according to Omar . Three of the dead were foreigners -- a Filipino , a Briton and a German , Omar said . State Department spokesman Mark Toner told CNN that two American contractors were among the wounded and had been taken to the Provincial Reconstruction Team hospital in Kunduz province . The six-and-a-half-hour attack was on an office of Development Alternatives Inc. , a humanitarian assistance subcontractor working with the U.S. Agency of International Development . The Taliban said the building was a base for U.S. Special Operations troops , which the U.S. military denied . DAI said four of the dead worked for its security subcontractor , Edinburgh International , and that several more EI staff were wounded as were two DAI staff members . In a conflicting report , Taliban spokesman Zabiullah Mujahid said six gunmen had killed nearly all of the 52 foreigners at the compound . `` The attack by insurgents in Kunduz was an attempt to intimidate Afghans and members of the international community trying to improve the lives of all Afghans , '' said NATO 's International Security Assistance Force in a statement . `` This attack shows the insurgents ' desire to prevent progress and draws attention to their true goal of serving themselves rather than the people of Afghanistan , '' said Navy Capt . Jane Campbell , an ISAF spokeswoman . `` We remain committed to serving alongside our Afghan partners to improve security and development for all Afghans . '' CNN 's Atia Abawi , Journalist Matiullah Mati and State Department Producer Charley Keyes contributed to this report .
NEW : Two of the wounded are Americans . The top U.S. commander arrives in Afghanistan on a day of more violence . Attack serves as reminder of a brazen insurgency , ISAF says . Pre-dawn attack targets subcontractor of U.S. aid agency .