His new title was predicted by analysts who had expected the 33-year-old chief would use the rare gathering to consolidate his grip on power.

The congress also announced it was strengthening the country's defensive nuclear weapons capability, putting the North's position on a more formal footing, and in defiance of UN sanctions.

His predecessors keep their posthumous titles - his grandfather, North Korean founder Kim Il-Sung is still "eternal president" and his father Kim Jong-Il remains "eternal general secretary".

Mr Kim and other senior party members took their seats, filling several rows on a stage at the April 25th House of Culture, below portraits of his two relatives.

Kim Yong-Nam, the head of North Korea's parliament, stood to read a roster of top party positions - calling Mr Kim chairman for the first time.

By gathering the congress together - something his father never did - Mr Kim's leadership style may be more like that of his grandfather, who used the party machine to get things done. His father preferred going through his own network of trusted individuals.

Trips around the capital

Mr Kim's promotion was announced as about 30 of 100 invited foreign journalists were allowed for the first time to view proceedings at the congress, which began on Friday.

A number of others were not allowed to attend the meeting, including a team from Sky News.

Officials have kept the foreign media busy with trips around the capital, showing them places the North wants them to see.

The sites included a textile factory named after Kim Jong-Suk, the wife of Kim Il-Sung and the current leader's grandmother.

They were also taken to a maternity hospital, electric cable factory and children's centre.

Meanwhile, three BBC journalists were expelled today for allegedly "insulting the dignity" of the country.

Pyongyang has said it was "a responsible nuclear weapons state" and vowed not to use them unless its sovereignty was threatened by a nuclear state.

Following nuclear tests earlier this year, the North was hit with tougher UN sanctions backed by its only major ally China.

Despite the penalties, the North has continued with its controversial project, and said it had developed nuclear warheads small enough to fit on missiles.

Western experts believe Pyongyang has about 40kg of plutonium, enough to build eight to 12 nuclear weapons.
North and South Korea are still in a technical state of war after their 1950-53 conflict ended in a truce, not a peace treaty.

The North regularly threatens its neighbour and major ally, the United States, which it accuses of planning a nuclear attack.