Friday's seizure comes a day after a small explosive device in a letter sent to a Kuwaiti editor detonated.
"The letters containing explosive material came from the same source in Lebanon which sent the letter to the editor of Al-Siyassa," communications ministry undersecretary Hamed Khaja said.
One letter was addressed to a journalist for Al-Siyassa, another to a colleague with the daily Al-Qabas, and the third to the secretary general of the Kuwaiti writers league, said Khaja.
A small explosive device in a letter addressed to Al-Siyassa's outspoken editor Ahmad al-Jar Allah blew up on Thursday as his secretary was opening it, causing him slight injuries.
Jar Allah, who owns the Al-Siyassa newspaper and its sister English-language Arab Times, said the device was contained in a letter addressed to him and sent from Beirut.
On opening it, the device blew up in Waleed Dahdooh's face. The secretary was treated for minor injuries to the face and hand, said Jar Allah, who was out of the country when the letter was opened.
The sender's name on the letter was that of Ghassan Sharbel, assistant editor of the pan-Arab daily Al-Hayat.
However, Sharbel and al-Hayat have both strongly condemned the attempt to associate them with the abortive attack on Jar Allah.
"We denounce the use of the paper's and my name to carry out such loathsome acts against journalists"
"We denounce the use of the paper's and my name to carry out such loathsome acts against journalists," Sharbel, a Lebanese, said.
Criticism of Islamists
He added he had no explanation for the use of his and his newspaper's name, but the incident was "detrimental to both Kuwait and Lebanon".
The communication ministry's Khaja did not further identify "the same source" supposed to be the sender of the three letters intercepted on Friday.
But press sources in Kuwait said the name of Sharbel and his newspaper had again been used by the would-be attackers.
Jar Allah, whose columns are regularly published on the front pages of both Al-Siyassa and the Arab Times, is well-known for his criticism of Islamists.
But Al-Siyassa last month also launched a scathing attack on the Syrian government for opposing the US-led occupation of Iraq.
The newspaper warned that Damascus could meet the fate of former Iraqi president Saddam Hussein, ousted in April.