Gunfire rang out in the Philippines Senate on Wednesday.

It sparked chaos in the building where authorities had tried to arrest a senator wanted by the International Criminal Court in connection with a deadly government crackdown on drugs.

It was not immediately clear who fired the shots or why.

No one was hurt, officials said.

The gunfire erupted as Philippine authorities tried to arrest Sen. Ronald dela Rosa, a former national police chief who enforced former President Rodrigo Duterte's anti-drug efforts in which thousands of mostly petty suspects were killed from 2016 to 2018.

Allied senators took Dela Rosa into "protective custody" on Monday, when he reappeared after months of absence.

Several senators were still in the building after holding a session when the gunshots were heard by a throng of journalists, including two from The Associated Press. Armed security personnel, including military members, ran around with guns ready and later asked employees to leave as tensions started to ease.

Senate President Alan Cayetano briefly appeared before journalists in the Senate shortly after the shots were fired but could not provide details.

"The emotions are high here," Cayetano said. "This is the Senate of the Philippines, and we are allegedly under attack."

Interior Secretary Juanito Victor Remulla Jr. later arrived with top police officials and said he was deployed by President Ferdinand Marcos Jr. to secure the senators. He said he did not come to arrest dela Rosa, who remained in the building.

Investigation launched

An investigation was underway, and security cameras would be reviewed to find out who was behind the gunfire and their intentions, Remulla said.

On Monday, the ICC unsealed an arrest warrant for dela Rosa.

Originally issued in November, the warrant charges dela Rosa with the crime against humanity of murder of "no less than 32 persons" between July 2016 and the end of April 2018, when he led the national police force under Duterte.

The ICC had no immediate comment on the events in Manila.

Dela Rosa, 64, has vowed to fight the ICC arrest order. He called on his followers Wednesday night to gather in the Senate to prevent what he said was his impending arrest.

National Bureau of Investigation agents tried to arrest dela Rosa on Monday, but he managed to dash to the Senate's plenary hall and sought the help of fellow senators. Cayetano said then that he would cite the government agents involved for contempt.

Duterte was arrested in March last year and flown to the ICC's headquarters in The Hague. He is still in detention in the Netherlands and faces a trial in the killings from his crackdown, in which dela Rosa has also been accused.

"We should not allow another Filipino to be brought to The Hague, the second one after President Duterte," dela Rosa said, addressing his followers in a Facebook message and blaming politics for his predicament.

"This is unacceptable," dela Rosa said.

He said he was ready to face any allegations before Philippine courts, but he denied condoning extrajudicial killings when he led the police force. Duterte has also made the same denials, although he openly threatened suspected drug dealers with death while in office.

Police deployed outside Senate

Hundreds of police officers have been deployed outside the Senate since Monday to maintain order, sparking complaints from dela Rosa and allied senators.

"If I have something to answer for, I will face those in our local courts and not before foreigners," dela Rosa told reporters in the Senate.

Five senators called on dela Rosa to surrender to authorities in a proposed resolution, but his allies opposed the move in a heated exchange Wednesday in the Senate, where 13 of 24 senators friendly to dela Rosa wrested control of its leadership on Monday.

Duterte and his daughter, the current vice president, and political allies such as dela Rosa have been the harshest critics of President Ferdinand Marcos Jr.

Vice President Sara Duterte, once a political ally of Marcos, has blamed the president for allowing what she said was "the kidnapping" of her father and his handover to a foreign court.

Sara Duterte has recently been impeached by the House of Representatives, which is dominated by the allies of Marcos, over accusations that included unexplained wealth and threats to have the president assassinated if she herself were killed amid their political disputes. The Senate was preparing to convene into a tribunal to try the vice president.

Disputes reflect deep division in Philippine politics

The disputes reflect the deep divisions that have long plagued the rambunctious Asian democracy.

After winning the presidency in 2016, Duterte appointed dela Rosa, a loyal ally, as head of the national police force, which enforced the brutal campaign against illegal drugs that alarmed Western governments, including the United States and human rights groups.

Dela Rosa also once headed the police force in the southern city of Davao, where Duterte was a longtime mayor and built a political name for his extra-tough approach to crime.

"My role was to lead the war on drugs, and that war on drugs was not meant to annihilate people," dela Rosa said when he was asked about the huge death toll.

"When the lives of police officers came under threat, of course they needed to defend themselves," dela Rosa said.

Duterte withdrew the Philippines from the ICC in 2019 in a move human rights activists say was aimed at escaping accountability.

The ICC, however, said that it retained jurisdiction over crimes committed when the Philippines was still a member and successfully moved to have him arrested, the first former Asian leader to fall into such disgrace.