Britain and France have both rejected a call by Italy for a pause in Nato‘s bombing of Libya to allow humanitarian aid to reach the civilian population.

The Italian foreign minister, Franco Frattini, had suggested that Nato’s credibility was at risk after a number of civilian casualties in air raids, but his comments were given short shrift in London and Paris, where both governments instead urged an intensification of pressure on Muammar Gaddafi amid signs that allied air attacks are moving into a new phase in western Libya. Nato also said that the operations would go on.

Britain and France are playing the leading military role in the three-month assault amid multiplying questions about its effectiveness, cost and sustainability.

David Cameron told MPs that UK forces were capable of keeping up the UN-mandated campaign for as long as necessary. “I think that is vital,” Cameron said, “and I would argue that the pressure is building on Gaddafi – time is on our side, not on Gaddafi’s side.”

Britain rebuffed the idea of a humanitarian pause, saying aid was already getting through due to actions to protect Misrata and other areas, and expressed doubts that Gaddafi would reciprocate. “It is Gaddafi’s continued refusal to stop brutalising his people, withdraw his troops and step down that is causing humanitarian problems in Libya,” the Foreign Office said. “He needs to go and go now.”

France echoed this position. “Any pause in operations would risk allowing [Gaddafi] to play for time and to reorganise,” said a foreign ministry spokesman in Paris. “In the end, it would be the civilian population that would suffer from the smallest sign of weakness on our behalf.”

The chorus followed the call by the outgoing head of the Arab League, Amr Moussa, for a ceasefire and a political solution that could leave Gaddafi in place. In a Guardian interview Moussa expressed reservations about Nato operations after credible reports of civilian fatalities.

Nato admitted earlier this week that a faulty missile had killed nine civilians, including children, in Tripoli. The Gaddafi regime claimed that 15 more civilians were killed in an attack on a compound that Nato confirmed it had targeted.

Frattini told Italian MPs: “With regard to Nato, it is fair to ask for increasingly detailed information on results as well as precise guidelines on the dramatic errors involving civilians.” Nato said it took the “utmost” care in targeting while Anders Fogh Rasmussen, its Danish secretary-general, insisted attacks would go on. “Nato will continue this mission because if we stop, countless more civilians could lose their lives,” Rasmussen said.

Moussa’s Guardian comments were dismissed by some diplomats as a bout of electioneering by a man who played a crucial role in providing Arab backing that paved the way for Nato intervention but is now preparing to contest Egypt’s first free presidential elections after the overthrow of Hosni Mubarak.

Libyan state TV and the official Jana news agency meanwhile reported that planes had carried out raids on checkpoints in the towns of Khoms and Nalut in western Libya. If confirmed this would mean the alliance had moved into a new stage of operations on roads leading into the capital Tripoli. Until now, Nato had limited itself to attacks on military installations and armour. Daytime airstrikes were also reported from Tripoli, where there were at least two explosions before noon as fighter jets soared overhead.

The Benghazi-based rebels were given a new diplomatic boost on Wednesday when China said it recognised the national transitional council as an “important dialogue partner”. China, like Russia, normally opposes moves it deems interference in the internal affairs of other countries and is unhappy with the Nato campaign. Its position suggests that despite Gaddafi’s defiance of demands that he step down, he remains isolated internationally.