Interfax news agency, quoting sources at Russia's military base of Mozdok in the neighbouring region of North Ossetia, said the rebels had also turned Grozny itself into a virtual fortress to ward off any possible storming of the city.
The agency said about 5,000 guerrillas were based in Grozny, where they were mining roads and buildings. It said their armoury included 10 armoured vehicles, two tanks, a multiple-rocket launcher and about 15 anti-aircraft guns.
The Chechen rebels' Internet web site reported renewed Russian aerial and artillery bombardment of Grozny, Argun and the town of Urus-Martan, which lies 25 km (16 miles) south of the capital.
Interfax said the rebels were clearly reluctant to surrender Argun without a fight, adding that around 400 fighters had moved to the town from Grozny, just 10 km (six miles) away, to help bolster its defences.
On Wednesday Defence Minister Igor Sergeyev said Argun had been sealed off and would likely fall to Russian forces in two to three days "with the help of residents".
Moscow, now into the third month of its Chechen campaign, is hoping the residents of Argun and Grozny will help expel the rebel fighters and let in the Russian forces, as has happened in several other Chechen towns.
But the Russian forces are expected to face a much tougher task recapturing Grozny, scene of fierce block-by-block fighting during the 1994-96 Chechen war, and mountainous areas in the south of the province where the rebels are traditionally strong.
Moscow accuses the Chechen fighters of trying to destabilise the North Caucasus region and of complicity in several bomb blasts in Russian cities.
- Reuters - Thomson Reuters Foundation
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