The head of Libya's interim government urged thousands of cheering supporters in the capital, Tripoli, late Monday to support a civil, democratic state that incorporates Islamic law into its principal legislation.

Mustafa Abdel Jalil called on Libyans to build a state based on the rule of law and avoid reprisal attacks against holdouts of former leader Moammar Gadhafi's government.

In his first public speech in Tripoli, the chairman of the National Transitional Council said his provisional administration seeks “a state of law, prosperity and one where Islamic Sharia law is the basis for legislation.”

He said “extremist ideology” on the right or the left would not be tolerated and that Libyans support a moderate version of Islam.

Jalil arrived in Tripoli Saturday for the first time since his allies chased Mr. Gadhafi out of the city. He addressed the rowdy crowd in Martyrs' Square, a site that until recently was used for pro-Gadhafi rallies. Jalil had been running the provisional government from the eastern city of Benghazi, cradle of the revolt that overthrew Mr. Gadhafi last month.

Earlier Monday, forces loyal to Mr. Gadhafi launched a series of counterattacks, including a surprise raid that killed 15 guards at a key oil refinery in the coastal city of Ras Lanuf.

A group of loyalist sympathizers working at the refinery set the facility on fire. The port was then targeted by a convoy of armed men. Ras Lanuf is deep inside NTC-controlled territory. Battles also continued near Mr. Gadhafi's hometown of Sirte and in parts of the oasis city of Bani Walid, southeast of the capital, Tripoli.

Also Monday, China officially recognized the NTC as the “ruling authority and representative of the Libyan people.” Algerian officials said late Sunday they would recognize the NTC as Libya's rightful authority once a “representative government is in place.”

Meanwhile, in neighboring Niger, government officials said 32 people close to Mr. Gadhafi have fled to the central African nation since September 2, including Mr. Gadhafi's son, Saadi. The U.S. State Department confirmed that authorities in Niger “are either in the process or have already brought” Saadi Gadhafi to the capital, Niamey, and intend to detain him.

On Sunday, Niger's justice minister said a convoy carrying 10 people, including Saadi, was traveling toward the northern city of Agadez where other Gadhafi loyalists are believed to have fled, including three generals and Mr. Gadhafi's security chief.

The justice minister said that Niger would fulfill its international obligations.

Moammar Gadhafi's whereabouts is still unknown. Late Saturday, Guinea Bissau's prime minister said his country would welcome the ousted leader should he seek exile in the West African country. Guinea Bissau had strong ties to Mr. Gadhafi's government when he was in power.

A message attributed to the former leader Monday urged Libyans to press ahead for his cause and not to surrender the nation to what he called “colonialism” and “foreign influence.”