US in new offensive on Taliban, al-Qaida

US bombers blasted the cavernous mountains of eastern Afghanistan for a third day today, pressing a new offensive against al-Qaida and Taliban fighters believed to be regrouping in the area.

One American and three US-allied Afghans were killed on Saturday and an unspecified number injured in the opening day of the ground attack.

Today’s airstrikes sent thick black plumes of smoke into the air above the Shah-e-Kot mountain range and shook the ground 20 miles away in Surmad, where a constant stream of B-52 bombers streaked overhead.

The bombardment was part of the largest known joint ground offensive of the war.

However, Saturday’s ground attack appeared to have made little headway in dislodging Taliban and al-Qaida fighters who fought back with artillery, mortars and heavy machine guns, Afghan officials said.

‘‘Firefights have been intense at times in heavy combat action,’’ Maj. A.C. Roper, spokesman of the 101st Army division in southern Kandahar, told reporters today.

A US defence official said a US-led force of 1,500 Afghan allies, US Special Forces and troops from the Army’s 101st Airborne assault troops had assembled for Saturday’s battle.

Canadian troops also were taking part, but not in large numbers, Canadian military spokesman Lt. Navy Luc Charron said.

Roper said the coalition forces were operating in cold, snow-covered mountainous terrain ranging from 8,300-11,600 feet above sea level.

After the ground attack stalled, US planes late on Saturday dropped newly developed bombs designed to send suffocating blasts through cave complexes, military officials said.

The ‘‘thermobaric’’ bombs were tested in December and officials said in January that they would be rushed to the region for the war.

Afghan forces broke off Saturday’s attack in the early afternoon and withdrew back to Gardez, 20 miles north of the assault.

Fighters recovering today at Gardez hospital described the operation as two-pronged, with one group of Afghan troops and US Special Forces launching a frontal attack and a second, travelling in rented pick-up trucks, attempting to ambush from the rear.

Fighter Mohammed Khan said the American was killed when a pick-up truck he was travelling in was hit by a mortar shell. Six of the injured were airlifted out of the area by helicopter, said a doctor at Gardez hospital, Naguibullah.

The rugged, caved mountains around Gardez have been a hiding place for Afghan warriors since anti-Soviet guerrillas used them as a base for their fight against Soviet troops in the 1980s.

Former Taliban front-line commander Saif Rahman was believed to be leading the Taliban and Taliban-allied foreign forces still in hiding there.

Neither the former Taliban supreme leader Mullah Mohammed Omar nor al Qaida chief Osama Bin Laden were believed to be in the area.