Hezbollah purchased same chemicals responsible for Beirut blast from Iran
The newspaper said it had seen invoices for the deliveries.
The massive explosion that ripped through large parts of Beirut on 4 August is said by authorities to have been triggered by a warehouse fire that set off large amounts of stored ammonium nitrate.
The hundreds of tons of the chemical had been confiscated years earlier and left unsecured for several years at the port, despite repeated warnings of the dangers it posed.
The powerful Shia group Hezbollah, which dominates parliament with its allies, stands accused of wielding great influence over Beirut's port and border posts.
Although Die Welt admitted there was no evidence that Hezbollah was responsible for the blast, it suggested that perhaps the group's interest in the material contributed to its presence at the port.
The explosion has also reignited claims that Hezbollah, which is designated by Washington as a terrorist group, stored arms at the blast site.
The Islamist movement's chief Hassan Nasrallah on Friday strongly denied the charges.
"We have nothing in the port: not an arms depot, nor a missile depot nor missiles nor rifles nor bombs nor bullets nor (ammonium) nitrate," he insisted.
Many Lebanese blame the blast on decades of corruption and negligence by Lebanon's ruling class - consisting largely of ex-warlords from its 1975-1990 civil war.
FBI personnel are to join other international experts already on the ground, including from France, which has launched its own probe.
Read more: Lebanon president says 'impossible' that Beirut port blast was caused by Hezbollah arms
Lebanese authorities too have opened an enquiry, despite scepticism at home over the credibility of a state-led investigation.
Public prosecutor Ghassan Oueidat has filed lawsuits against 21 suspects over the blast, 19 of whom are already in custody.
Judge Fadi Sawan, who was appointed Friday to lead investigations, is to start interrogating suspects next week.
Agencies contributed to this report.
Follow us on Facebook, Twitter and Instagram to stay connected