France has stepped up its probe into the massive Beirut port blast last week by handing it to investigating magistrates, prosecution sources said Friday, as it was confirmed two French citizens were among the 171 people killed.

The investigation has now been entrusted to two magistrates who can ultimately decide whether to press charges over the August 4 blast, a source in the office of the Paris prosecutor told AFP.

U.N. human rights experts have demanded a swift, independent investigation into the catastrophic Beirut explosion, citing deep concern about irresponsibility and impunity in Lebanon.

Arriving in Lebanon after last week's deadly Beirut blast, U.S. envoy David Hale bypassed politicians to head straight to a hard-hit neighborhood where young volunteers are helping people abandoned by their state.

Lebanon's judicial investigation of the Beirut port explosion started with political wrangling over the naming of a lead investigator, military threats to jail leakers and doubts over whether a panel appointed along sectarian lines could be fully impartial.

So for many Lebanese, their greatest hope for credible answers about the blast that wrecked much of their capital may lie with outsiders. Families of the dead and survivors on Friday asked the U.N. Security Council for an international investigation. Others pin their hopes on the French forensic police who have joined the probe and FBI investigators are expected to take part.

Ten days after the deadly Beirut explosion, rescue workers recovered the remains of firefighters killed while battling the initial blaze, as authorities appointed a well-respected judge to lead the investigation.

Iranian Foreign Minister Mohammad Javad Zarif said Friday that Western countries should not take advantage of the massive explosion in Beirut last week that killed and injured thousands of people to dictate their own policies on the tiny Arab country.

Zarif's comments came in Beirut as a senior U.S. official and France's defense minister were in the country. The Aug. 4 blast at Beirut's port killed nearly 180 people, injured 6,000 and caused widespread damage in the capital.

U.S. Under Secretary of State for Political Affairs David Hale met with senior Lebanese officials on Friday, one day after arriving into Lebanon and bypassing politicians to head straight to a hard-hit neighbourhood where young volunteers are helping people after the colossal Beirut blast

Representatives of the victims killed in Beirut blast on Friday expressed mistrust in a state-backed probe into the deadly colossal explosion, demanding international investigation.

The death toll from last week's massive explosion in Lebanon's capital has risen to nearly 180, with an estimated 6,000 people injured and at least 30 missing, the United Nations said Friday.

The explosion has affected operations at six hospitals, up from an initial three, and damaged more than 20 clinics in the parts of Beirut worst hit by the blast, the U.N.'s humanitarian affairs agency said in its report.

Lebanon's judicial investigation of the Beirut port explosion started with political wrangling over the naming of a lead investigator, military threats to jail leakers and doubts over whether a panel appointed along sectarian lines could be fully impartial.

So for many Lebanese, their greatest hope for credible answers about the blast that wrecked much of their capital may lie with outsiders: the French forensic police who have joined the probe and FBI investigators are expected to take part.