China's top security official has made the first high-level trip to Afghanistan by a senior Chinese leader in nearly half a century, meeting President Hamid Karzai in Kabul.
Zhou Yongkang made the four-hour visit on Saturday, in a secretive trip aimed at shoring up ties between the neighbours, China's Xinhua news agency reported.
Karzai's office said Zhou came to the war-battered nation to discuss the implementation of a strategic cooperation agreement that Karzai signed with his Chinese counterpart Hu Jintao in June.
During a meeting with Zhou in his Kabul palace, Karzai said "China is a good and honest friend of Afghanistan," his office said in a statement.
Beijing has stepped up diplomacy with Afghanistan in recent months as the 2014 deadline for the withdrawal of US and NATO troops approaches.
China, which shares a 76-kilometre (47-mile) border with Afghanistan's far northeast, has already secured major oil and copper mining concessions in Afghanistan, which is believed to have more than $1 trillion worth of minerals.
Karzai urged China to further invest in his poverty-stricken nation's underground treasures, the palace statement said.
The scramble for influence in Afghanistan is expected to intensify in the run-up to 2014, with its central position in a volatile region having shaped its history for centuries.
Xinhua provided few details about the visit, other than quoting Zhou as saying: "It is in line with the fundamental interests of the two peoples for China and Afghanistan to strengthen a strategic and cooperative partnership... conducive to regional peace, stability and development."
The visit was not previously announced due to security concerns. Late president Liu Shaoqi, the last senior Chinese official to visit Afghanistan, visited in 1966, Xinhua said.
Zhou, ranked ninth in China's ruling Communist Party hierarchy, is China's top security official and oversees a crackdown on religious extremism, terrorism and separatism in his nation's Muslim-populated Xinjiang region, which borders Central Asia and Afghanistan.
Zhou's appearance in Kabul comes after Karzai pledged to work with China to fight terrorism and extremism in the region during a visit to Beijing in June, where he attended the Shanghai Cooperation Organisation meeting.
The grouping, which is led by China and Russia and was set up to counterbalance US and NATO influence, granted Afghanistan observer status at the meeting.