U.S.-backed Afghan rebels captured a strategic valley near the eastern city of Jalalabad, but last week's snow and heavy rain restricted guerrilla operations elsewhere in Afghanistan, a Western diplomat said Tuesday.

Afghan President Najibullah, meanwhile, reportedly said Pakistani regular army units were helping rebels fight for strategic Jalalabad and warned Pakistan those who "pour oil on the fire" could suffer in "the flames of this war."The Western diplomat said the rebels last week seized a key military post a few miles south of Jalalabad, 70 miles east of Kabul, giving them control of the Chapryhar valley, including firing positions that overlook Jalalabad's airport.

The envoy also said the guerrillas have resisted attempts by the pro-Soviet government to dislodge them from a section of road between Kabul and Jalalabad. He said troops inside Jalalabad have cut down on their artillery attacks.