Nato has denied a Libyan government charge that it is intentionally using its air strikes to help rebel advances, saying it is sticking to its mandate to protect civilians.
Wing Cmdr Mike Bracken, a Nato spokesman in Naples, Italy, said it is "not involved in the ground battles", although he acknowledged the alliance is tracking the fighting between rebels and forces loyal to Muammar Gaddafi.
Libya's deputy foreign minister Khaled Kaim accused Nato of intensifying its bombing campaign and backing foreign mercenaries to lay the groundwork for an advance by rebels trying to topple Gaddafi's regime.
He claimed increased bombings in recent days represent the "final phase" of Nato's air campaign. But he said the push will fail and that civilians will pay the price.
Mr Kaim said Nato targeted police checkpoints in the Nafusa mountains south-west of Tripoli ahead of a rebel advance toward the village of Qawalish, which rebel fighters said they seized on Wednesday.
A fuel depot in the key eastern oil town of Brega was also destroyed, he said. Nato said it hit equipment used to refuel government military vehicles.
The intensified barrage of air strikes, particularly in the west of the country, is focused on targeting civilian infrastructure and police checkpoints, he said.
"The aim of these attacks is to help the rebels to advance. But I assure you, it will be another failure for them," he said.
Mr Kaim also claimed Libyan forces have evidence that Colombian mercenaries funded by the West and its Arab allies have joined the rebel fighters trying to advance toward the capital Tripoli from the western rebel-held city of Misrata.
Nato spokeswoman Oana Lungescu said: "We've not seen anything to indicate this allegation might be true. But what we have seen are repeated consistent and credible reports that Gaddafi's forces have been using mercenaries, not just now or in recent months but for years and decades."