Libyan leader Moammar Gadhafi has vowed to fight to the end, after NATO aircraft pounded Tripoli on Tuesday with some of the most intense daytime airstrikes since it began its campaign.

Mr. Gadhafi made the vow in a fiery audio speech that was broadcast on state television. He said the Libyan people will not “kneel” and will not surrender.

Earlier Tuesday, a long series of explosions caused by the airstrikes rocked the Libyan capital. Witnesses said they saw smoke in the area of Mr. Gadhafi's sprawling compound in the city.

Meanwhile, world powers are increasing pressure on Mr. Gadhafi's government. The European Union announced on Tuesday that it plans to add six Libyan ports under the government's control to its sanctions list.

Also, Russian envoy Mikhail Margelov met with members of the opposition Transitional National Council in the rebel stronghold, Benghazi. He said Moscow is interested in Libya being a sovereign and democratic country that is a “worthy member of the international community.”

China's Foreign Ministry said one of its diplomats based in Egypt recently held talks with the Libyan rebel council. Libya's foreign minister is on a three-day visit to Beijing.

China and Russia both abstained when the U.N. Security Council voted in March to establish a no-fly zone over Libya, and they have called for a negotiated solution to the conflict.

In Brussels, NATO Secretary-General Anders Fogh Rasmussen said he would use a defense ministers' meeting Wednesday to repeat calls for the alliance to step up involvement in the Libya operation.