WASHINGTON - The United States tightened financial pressure on Libyan leader Muammar Gaddafi on Friday, adding five senior Libyan government officials and two entities controlled by Gaddafi's children to its sanctions blacklist.

The US Treasury Department said it added Libya's prime minister, Ali al-Mahmoudi Al Baghdadi, and Gaddafi's chief of staff, Bashir Salehand, to the sanctions blacklist.

Related readings:  General: US may consider sending troops into Libya  Libya takes Britain to task over key oilfield bombing  NATO denies bombing Libya's largest oil field  Libya contact group to meet in Doha on April 13

The sanctions, now against 19 individuals, prohibit US transactions with them and seek to freeze any assets they may have under US jurisdiction.

To date, the United States has frozen more than $34 billion of Libyan government assets.

"We will continue to expose and impose sanctions on senior Libyan government officials who choose to remain at Gaddafi's side," said David Cohen, the acting under secretary for terrorism and financial intelligence.

"They have a choice to make, and we will make that choice as stark as possible," he said in a statement.

Treasury has shown a willingness to lift sanctions against those who sever ties with Gaddafi's regime. Early in April, it did so with former Libyan foreign minister Moussa Koussa, who defected and is now cooperating with British authorities.

Also blacklisted on Friday were Libyan Finance Minister Abdulhafid Zlitni, the country's oil minister, Shukri Ghanem, and Libya's internal security director Tohami Khaled.

The Gaddafi International Charity and Development Foundation, a Geneva-registered entity owned by Gaddafi's son Saif Al Islam, and the Waatasemu Charity Association, controlled by his daughter, Aisha, were sanctioned, Treasury said.

The Obama administration, which has called for Gaddafi to leave but has insisted the United States will not use military force to oust him, is considering using some of the frozen assets to pay for humanitarian needs in the country.