• Customs director-general Badri Daher has been in police custody for more than 10 days following the massive blast.
• The explosion killed over 170 people, and left scores others injured.
• Daher was questioned by Judge Fadi Sawan prior to being formally arrested.

A Lebanese judge leading investigations into Beirut's port blast issued a preliminary arrest warrant Monday against customs director-general Badri Daher, a judicial source told AFP.

Daher has been in detention for more than 10 days over the 4 August explosion that killed 177 people, wounded at least 6 500 others and devastated swathes of the capital.

The detonation of a huge stock of explosive ammonium nitrate stored unsecured in a portside warehouse for years has been widely blamed on official negligence and corruption.

The judge overseeing the investigation, Fadi Sawan, questioned Daher for four hours before issuing the warrant, the judicial source said.

Lebanese law allows suspects to be detained and questioned prior to being formally arrested. It was not immediately clear what charges Daher was being held on.

Public prosecutor Ghassan Oueidat had filed lawsuits against 25 suspects over the Beirut blast, 19 of whom are already in custody.

Those detained include Beirut Port's general manager, Hassan Koraytem, who will be questioned by Sawan on Tuesday.

Former Lebanese customs director Shafic Merhi, port security head Mohammad Al-Awf and port warehouse manager Michel Nakhoul will also be interrogated.

Western powers and international bodies as well as Lebanese at home and abroad have called for an international probe into the blast.

Lebanese authorities have rejected an international inquiry.

US FBI investigators arrived in Lebanon at the weekend at the request of Lebanese authorities to assist with the probe.

France has already opened its own investigation.

Lebanese authorities also extended until 18 September a state of emergency declared in the aftermath of the blast, which had been set to expire in the coming days.