Kabul Correspondent William Reeve: "The offensive has been expected for many months"

On Wednesday morning, the Taleban attacked the forces of opposition commander Ahmad Shah Masood in the Tagab Valley, 75km north-east of Kabul.

A second attack was launched along what's called the New Road, leading north from the capital towards Bagram airbase.

Unconfirmed reports say the Taleban have advanced 2km along the Tagab Valley; on the other front they are reported to have taken some high ground.

Ahmad Shah Masood is the main opposition commander

The Afghan Islamic Press reported that "fierce fighting was reported at both fronts with the use of artillery and heavy weapons".

Opposition forces fired three rockets at Kabul's civilian and military airport on Wednesday morning but added there were no reports of damage. Aid flights were diverted or cancelled on Tuesday after opposition fighters fired rockets at the airport.

Talks fail

The offensive comes a week after UN-sponsored peace talks in the Uzbek capital, Tashkent, ended without any progress towards a settlement between the two sides.

UN special envoy Lakhdar Brahimi warned then that arms were "pouring" into Afghanistan from neighbouring countries and urged the Taleban and its foes to declare a halt to three years of war.

In August 1998, the Taleban pushed north and captured the city of Mazar-e Sharif near the Uzbek border. They now control 90% of the country, but there has been no serious fighting for 10 months.

The opposition released a statement at the weekend warning that it would treat any foreign recruits it captured in Taleban ranks as criminals and give them "maximum punishment".