THE HAGUE (Reuters) – NATO members should supply more warplanes to bomb Libyan military targets, the alliance’s secretary general said on Thursday, increasing pressure on states to contribute more to the mission.

Western powers have become embroiled in a conflict in the oil-producing North African state, straining resources and relations among NATO’s 28 members after only four months of a United Nations-mandated campaign meant to protect civilians from attacks by Muammar Qadhafi’s regime.

NATO chief Anders Fogh Rasmussen, who met Dutch Prime Minister Mark Rutte on Thursday, called on the Netherlands and other members of the alliance to consider their contributions to the mission, stressing the need for air-to-ground strikes.

“We can’t protect civilians in Libya effectively if we are not prepared to take out critical military units on the ground that can be used to attack civilians. This is the reason why we do air-to-ground strikes,” Rasmussen said.

“I encourage all allies that have aircraft at their disposal to take part in that operation as well,” Rasmussen said in the Hague after a meeting with Rutte.

“I hope the Dutch government, like all other governments, will continuously consider adaptations of the strategy.”

The Netherlands recently extended its contribution to the Libya mission by three months, but Rutte said on Thursday Dutch planes will not take part in bombing Libyan targets.

“I fully understand NATO which wants the countries participating in the mission to be as flexible as possible. That’s perfectly logical,” Rutte said.

“But at the same time we have to take into consideration our assessment of the situation and our political support for the decision. We are not against air-to-ground bombings, but the Netherlands at the moment is not participating.”

The Dutch minority coalition relies on the support in parliament of the Freedom Party, a populist, anti-Islam party headed by Geert Wilders who strongly opposes Dutch participation in foreign conflicts and financial bailouts.

The previous government fell in early 2010 over whether to pull troops out of Afghanistan and within months, Dutch soldiers had been brought home.

British Defence Secretary Liam Fox on Wednesday said some European NATO members were not pulling their weight in the Libyan air campaign.

His comments echoed those of former US defence Secretary Robert Gates, who in a valedictory speech in June said European NATO members risked “collective military irrelevance” if they did not deepen their commitment and boost spending.

On Thursday, a British military source said Britain was running short of military targets in Libya, rather than running short of resources.

Norway, one of the first European states to signal its willingness to participate in the Libya mission, started to wind down its role in the air strikes last month, an indication its appetite for further missions has waned since it became apparent how difficult it will be to overthrow Qadhafi.