Nasser Judeh, the Jordanian government spokesman, said on Wednesday that the arrests were connected to the discovery on April 18 of a cache of weapons, including Iranian-made Katyusha rockets and anti-tank missiles, that were allegedly smuggled into Jordan and stockpiled there.
Judeh said that since the discovery, 20 Hamas activists had been detained, and investigations could reveal more people involved in a plot "targeting locations, military and civilian officials".
The government suspects that more hidden weapons have yet to be found, constituting a "great danger to Jordan's national security", he said.
Judeh also said that state television would air confessions by the detained activists on Thursday to address public suspicions about the accusations.
On Wednesday, Jordanian authorities briefed five top Palestinian security officials, led by Major-General Tareq Abu Rajab, chief of Palestinian General Intelligence, of the evidence against the Hamas members.
The team was sent by Mahmoud Abbas, the Palestinian president, not the Hamas government.
Judeh said the Palestinian team was being shown "secret documents, information and evidence which implicates [Hamas] beyond doubt".
He said Hamas had been seeking to "recruit elements to operate" in the kingdom as well as bring in activists from the Palestinian territories "to send them to Syria and Iran for training on intelligence, security and military activities".
The government has said in the past the weapons were smuggled from neighbouring Syria.
Hamas officials and the Syrian government, which hosts exiled Hamas leader Khalid Mishal, have denied the accusations.