Defence Minister Nikolai Svinarov told reporters after a security council meeting in Sofia on Friday that contact had not yet been established with the captors.
"Firstly, we will try to extend the deadline which expires at 11pm tonight [2000 GMT on Friday]," he said. "The situation is very difficult."
A firm supporter of the US-led invasion of Iraq, the new NATO member state currently has 470 troops stationed in the southern Iraqi city of Karbala.
Bulgarian Prime Minister Simeon Saxe-Coburg said his country was doing all it could for its nationals, without ruling out negotiating with the captors who threatened to kill them.
Simeon Saxe-Coburg (L) stressed
the need to keep channels open
Saxe-Coburg told reporters in Belgrade it was necessary in such situations to "engage all possible channels, means and connections".
But his foreign minister, Solomon Passy, made clear Bulgaria's staunchly pro-US policy would not change as a result of the kidnapping.
"Bulgaria is a stable state with a predictable foreign policy and we cannot expect it would change its foreign policy because of one or another group," Passy told state radio.
The hostages' wives arrived in Sofia and were meeting Passy
while the company which employed the men said it was suspending operations in Iraq.
Bulgaria's Foreign Ministry identified the two captives as civilian truck drivers Ivailo Kepov and Georgi Lazov and said they had left for Iraq on 19 June.
Their captors threatened on Thursday to kill them in 24 hours unless US-led forces freed prisoners, Aljazeera television reported. A broadcast videotape appeared to show the two captives sitting in front of masked captors.
Aljazeera said the tape came from the Tawhid and the Jihad group headed by Jordanian Abu Musab al-Zarqawi, who has been accused by Washington of links to Usama bin Ladin's al-Qaida.
"We cannot expect it (Bulgaria) would change its foreign policy because of one or another group"
foreign minister, Bulgaria
The two drivers were taken hostage after delivering cars to the northern Iraqi city of Mosul, state radio said.
They worked for a small Bulgarian transport company, Dimitrova-Stoimenov-Gracia-Eva, which said it was supplying second-hand cars under a contract with an Iraqi businessman.
"We are now stopping operations in Iraq," company manager Ivan Stoimenov told the radio.
The kidnapping comes three months after a Bulgarian driver was killed in an attack on a convoy of trucks between Basra and Baghdad.