"I can't say specifically what weapons we have found. We can say they have not been registered in the Czech Republic," he added.
The website of mass circulation Respekt weekly quoted unnamed police sources as saying Jamal had probably mishandled a bomb hidden in the safe at his Prague home.
It said police had found automatic rifles and other illegal weapons that could arm a 10-man combat unit.
Jamal, 56, who had been in the post since October, suffered fatal injuries to his head, chest and stomach.
His 52-year-old wife was treated for smoke inhalation but discharged from hospital Wednesday.
Palestinian foreign minister Riyad al-Malki described the blast as "a work accident".
"The safe was old, and it was made in a way that if it is being opened in a wrong way, an explosive device attached to its door would explode, and this is what happened.
He told Voice of Palestine radio that Jamal had opened the safe "without consulting with anyone" but that no crime had been committed.
'Safe in everyday use'
But Palestinian embassy spokesman Nabil al-Fahel told AFP the safe was in almost everyday use and "according to our information there was no built-in anti-theft system".
Jamal was a member of the ruling Palestinian Fatah party of president Mahmud Abbas. He served as a diplomat in Bulgaria and Egypt as well as then Czechoslovakia during the communist era.
The Czech Republic is a staunch ally of Israel but Prague has hosted a Palestine Liberation Organisation (PLO) mission since 1981, when it was the capital of Czechoslovakia.
The mission became an embassy in 1988, but in November 2012 the Czech Republic was one of nine countries which voted against the UN General Assembly move to upgrade the Palestinians' status to non-member observer state.
When Jamal began his mission, he asked President Milos Zeman to rescind his controversial call for the Czech embassy in Israel to be moved from Tel Aviv to Jerusalem.
The blast occurred on the eve of a new visit to Israel and the Palestinian territories by US Secretary of State John Kerry to push faltering peace talks.
"I think the Palestinian administration should explain many questions related to the explosion," security expert Andor Sandor, the former head of Czech military intelligence, told AFP.
"First, why do they breach the Vienna Convention setting rules for diplomatic relations and activities, second, why diplomatic immunity is being abused for activities that cannot be considered legal," he said.
"Another question is whether they have more safes like this on Czech territory, in their flats, and who installs such systems there," Sandor added.
Zoulova told AFP it was "definitely not standard to have an arsenal of weapons or explosives in such a building".
"This is a question the police are dealing with within the investigations," she said.
Born in Beirut in 1957, Jamal joined Fatah in 1975 and became an aide to the ambassador in Bulgaria four years later. He moved to Prague as a diplomat in 1984.
After working as Palestinian consul to the Egyptian port city of Alexandria from 2005, he was appointed ambassador to the Czech Republic in October 2013.