Air force jets bombed rebel targets in northwestern Macedonia in one of the few aerial attacks in the government's six-month conflict with ethnic Albanian rebels, witnesses and diplomats said.
This is a serious escalation of the fighting, a diplomat said. No official comment was immediately available.
He said Sukhoi SU25 aircraft made two sorties and hit targets in the area around the villages of Tearce and Neprosteno, north of Macedonia's second city Tetovo.
Witnesses also saw bombs fall on targets further north near the Kosovo border.
Meanwhile, the signing of peace deal by Macedonia's political parties aimed at averting civil war could be jeopardised by renewed fighting, the EU's chief envoy to Macedonia said.
"I remain very cautious. If the situation on the ground continues to deteriorate, what has been agreed and concluded on paper could be thrown into question," Mr Francois Leotard said.
Mr Leotard's comments came a day after ethnic Albanian rebels launched their deadliest attack yet on Macedonian forces since the guerrillas took up arms against the Skopje government six months ago.
Despite that ambush, which killed 10 soldiers, negotiators managed last night to draw up an agreement to end the conflict between Macedonians and their large ethnic Albanian minority.
Mr Leotard, who was at the talks in the resort of Ohrid, said afterwards the Western-backed agreement should be formally signed on Monday.
He also said there had been no guarantees the rebels would observe the accord. They are not taking part in the talks.
The EU envoy also said the necessary preconditions for the deployment of a 3,500-strong NATO force in Macedonia to oversee the disarming of the rebels were not yet in place.
"NATO will not deploy until there is a real ceasefire," he said.
AFP