NATO war planes on Sunday continued their assault on targets in and around Tripoli, hitting a military barracks in the Libyan capital and checkpoints near Brega.

The attacks are designed to keep up pressure on Libyan leader Moammar Gadhafi to bring to an end his 42 years in power.

British Foreign Secretary William Hague, who visited the rebel stronghold of Benghazi on Saturday, said the campaign against pro-Gadhafi forces is intensifying. But he rejected suggestions that it has strayed from the U.N. mandate to protect civilians.

He told reporters in London Sunday, “This is not mission creep .”

Hague defended the use of British and French attack helicopters, which were employed for the first time on Saturday. But Russian Deputy Prime Minister Minister Sergei Ivanov warned that use of the helicopters puts NATO “one step” closer to a ground operation.

Russia abstained when the U.N. Security Council voted in March to establish a no-fly zone over Libya. It has repeatedly called for a negotiated solution to the conflict.

A special Russian envoy is due Monday in Benghazi, where he plans to meet with members of the rebel Transitional National Council.

Meanwhile, Iman al-Obeidi, a Libyan woman who claimed she was gang-raped by Mr. Gadhafi's troops, is said to be on her way to the United States. Marwa al-Obeidi said her sister was flown out of the eastern rebel stronghold of Benghazi early Sunday.

The Associated Press reported that Marwa al-Obeidi told reporters a human rights group aided by U.S. Secretary of State Hillary Clinton arranged for Iman and their father to travel in a private plane to Washington by way of Malta and Austria.

Al-Obeidi was forcibly deported last week from Qatar to the eastern rebel stronghold of Benghazi. She burst into a Tripoli hotel in March to tell foreign journalists she had been raped by government troops, saying she was targeted because she is from Benghazi. Her rape claim could not be independently verified.