Senator Antonio Trillanes has criticised the president’s anti-drug war and challenged him to explain his wealth.

Philippine President Rodrigo Duterte has ordered the arrest of his fiercest critic in Congress after revoking the senator’s amnesty for involvement in unsuccessful military uprisings years ago.

Senator Antonio Trillanes condemned Duterte’s move, which was made public on Tuesday, as illegal and “a clear case of political persecution”.

After Senate leaders assured they would not allow his arrest in the Senate, Trillanes said he would stay in the building while police officers waited outside in a looming standoff.

“We’re living basically in a de facto martial law environment of the ’70s kind,” Trillanes told a throng of journalists and supporters, referring to martial law declared by dictator Ferdinand Marcos in 1972, which is regarded as a dark chapter in Philippine history.

Trillanes has repeatedly questioned Duterte’s deadly drug war, and challenged the president to explain his alleged “hidden wealth”.

He also presented before the Senate witnesses who accused the president of being directly involved in extrajudicial killings.

Amid political tensions over the arrest order, some opposition politicians and followers visited the Senate to show support for Trillanes.

The 47-year-old former navy officer was detained for years before his election to the Senate for involvement in three military revolts from 2003 to 2007 protesting official corruption under the presidency of Gloria Arroyo, now House Speaker and a Duterte ally.

‘Bending the law’

Trillanes received amnesty under Duterte’s predecessor, Benigno Aquino III. Several young military officers who were detained for joining failed coup attempts and uprisings against Arroyo were also granted amnesty. But only Trillanes’ was revoked so far.

In an interview with the news website Rappler, Aquino said the amnesty he extended to Trillanes “must be respected and recognised” by the Duterte administration.

Trillanes said his lawyers would petition the Supreme Court to fight the move by Duterte, who is on a visit to Israel.

“They’re bending the law to be able to do their political objective, which is to persecute the political opposition,” Trillanes said.

Justice Secretary Menardo Guevarra told a news conference that Duterte signed a proclamation last week voiding Trillanes’ 2011 amnesty, because the senator had failed to comply with all of its requirements – including a clear admission of his involvement in past coup attempts.

Trillanes cannot invoke his congressional immunity from arrest because the crimes he allegedly committed, including rebellion, were serious and punishable by life imprisonment, the justice chief said.

During a televised Senate session, however, Trillanes showed proof refuting that claim.

Presidential spokesman Harry Roque told reporters in Israel the move against Trillanes was not political persecution, saying the government was just enforcing the law.

But Vice President Leni Robredo said the arrest order sends a chilling effect to the critics of the Duterte administration.

Another opposition senator and Duterte critic, Leila de Lima, is also under police detention.