Militants in a surprise move penetrated a UN guesthouse in the fortified Afghan capital Kabul Wednesday morning, killing six foreign national staff of UN, a police officer said.

"The militants entered the guesthouse at 5 a.m. local time in the Shirpoor diplomatic enclave and began firing and suicide attack, killing six staff on the spot," the officer told Xinhua but declined to be named.

He also added that three security guards of the compound were also killed in fire exchange with the intruders.

The guesthouse, according to the officer, accommodated the international staff of United Nations Assistance Mission in Afghanistan (UNAMA).

The spokesman of Interior Ministry Zmarai Bashari confirmed three suicide bombers have been killed so far.

Meantime, another police officer at the site on the condition of anonymity said five more UN staff were injured.

Taliban spokesman Zabihullah Mujahid in talks with media from undisclosed location via telephone claimed responsibility, adding three insurgents attacked UNAMA to disrupt the runoff vote.

Taliban outfit in a statement released to media a week ago vowed to derail the second round presidential polls set for November 7. The militants also asked Afghans to boycott the process.

Moreover, two rockets reportedly hit the capital city as one landed on the only five-star hotel Serena in Kabul and the other exploded near the building of Foreign Ministry, no report of the casualties so far.