Afghan officials say a group of suicide bombers dressed in police uniforms killed seven people and wounded 12 others in an attack on a government compound in western Afghanistan.

Authorities say four attackers equipped with explosive vests, guns and rocket-propelled grenade launchers stormed the governor's compound in Farah Province Thursday. At least one of the attackers blew himself up at the gate and the rest launched an extended gunbattle with police.

All of the attackers died in the incident, as well as six police officers and one civilian.

There were no immediate claims of responsibility for the attack, but it comes less than a month after a similar attempt to assassinate the governor of Kandahar Province took place.

These attacks are the hallmark of the Afghan Taliban, which announced the start of its annual spring offensive earlier this month.

NATO already has transferred security control of large portions of Afghanistan to local authorities, and most of the 130,000-strong foreign force is set to leave the country by the end of 2014.

Afghan President Hamid Karzai and the leaders of the foreign donor countries are meeting in the coming days for a NATO summit in the United States. They are expected to finalize details of the withdrawal and outline future international assistance to the war-torn country.

Ahead of the summit, the research group Afghanistan Analysts Network released a new report cautioning that NATO's Afghan policy must be flexible in order to achieve long-term security goals in the country.

Researchers tell VOA that the Western alliance must focus not only on the Afghan army and police force, but also ensure that political institutions and development projects are in place.