The United States says the Libyan rebel's transitional national council has accepted an invitation from President Barack Obama to open a representative office in Washington. Assistant Secretary of State Jeffrey Feltman said today said the U.S. considered the opposition council as the legitimate representative of the Libyan people. The high-ranking U.S. diplomat is on a three-day visit to Libya and is the most senior U.S. official to visit the country since the uprising against Mr Gadhafi began in February. The diplomatic invitation comes as NATO warplanes rocked the Libyan capital, Tripoli, with some of its heaviest airstrikes yet. According to witnesses, at least 15 explosions were heard in the city on Tuesday as NATO warplanes roared overhead . A Libyan government spokesman said the latest strikes killed at least three people and wounded dozens more.