KABUL, Afghanistan (AP) _ An Islamic rebel group threatened Thursday to scrap a cease-fire agreement with the government and renew its shelling of the city's airports.

Hezb-e-Islami accused ''Communist generals and uncivilized militia'' loyal to the 4-month-old government of attacking its bases in western and northern Afghanistan.

Unless the assaults stop immediately, Hezb-e-Islami will attack Kabul's joint civilian-military airport and prevent flights from landing or taking off in the capital, the rebel group said in a statement.

The airport was shut down last month by relentless rocket bombardment that destroyed the control tower and the navigation system. Flights resumed a week ago.

Hezb-e-Islami also threatened to shell Bagram, the military airfield 15 miles north of Kabul.

Hezb-e-Islami's chief, Gulbuddin Hekmatyar, signed a truce Aug. 28 and halted a month of rocket and shelling attacks that killed at least 1,900 people, injured thousands more and drove hundreds of thousands from the terrorized city.

The truce has allowed Kabul's 1 million residents to move freely around the city, but most are convinced it won't last.

Since assuming power from the former Communist regime in late April, the Islamic government has been beset by differences among its component groups. The ethnic, religious and power disputes have frequently turned Kabul's dusty and rutted streets into battlefields.

The government has signed one cease-fire after another, but each has collapsed within weeks.

The government claims Hekmatyar currently is rearming and regrouping his forces on the southern and eastern edges of the city.

Hekmatyar, who advocates a strict Islamic ideology, as alien to Afghans as communism, was expelled from the Islamic leadership last month because of his rocket attacks on Kabul.

Hekmatyar opposes the presence in the capital of former army officers and militia that had supported the Communist government in its 14-year war against the Muslim resistance.

Although many switched sides and helped the rebels bring down the former regime, Hekmatyar wants them removed and has threatened to attack the city until his demands are met.