Suicide bombers tried to strike two oil facilities in Yemen with explosives-packed cars, but authorities foiled the attacks and four bombers and a security guard were killed, the government said Friday.

The attempts came ahead of this week's presidential elections, in which President Ali Abdullah Saleh faces a serious challenge for the first time since he became head of state in 1978.

They also came days after Al Qaeda's No. 2, Ayman al-Zawahiri, issued a videotaped threat of attacks on the Persian Gulf and on facilities he blamed for stealing Muslim oil.

Countrywatch:Yemen

Friday's attacks happened 35 minutes apart, targeting a Yemeni oil refinery in the northeast province of Mareb and a Canadian-Yemeni oil storage facility at the Dubba Port in Haramut province — scene of a 2002 attack on the French tanker Limburg, an Interior Ministry statement said.

The statement said an investigation was under way to determine the identity of the "terrorist elements" behind the attacks.

Fourteen of 23 Al Qaeda prisoners who escaped from jail in February remain still at large. The escape raised questions about Yemen's reliability in the fight against terrorism.

The Interior Ministry said the attacks would not stop Yemen from "continuing its persistent efforts to fight terrorism and the terrorist elements of darkness that are trying to undermine the security and stability of the country and its interests."

Yemen is the ancestral homeland of Al Qaeda leader Usama bin Laden and was the scene of the 2000 bombing of the destroyer USS Cole that killed 17 American sailors.

In the first attack, two suicide bombers drove "at great speed" toward the Dubba Port at 5:15 a.m. in an attempt to blow up storage tanks containing a "huge amount" of oil, the ministry said.

The driver of the first car was wearing a uniform similar to those worn by staff at the facility, and the second driver was dressed in a military uniform, the statement said.

It said guards at the port "managed to blow up the rigged cars before they reached their targets."

A security guard was killed while "remains of the two terrorist attackers were strewn all over the place," the statement said. Shrapnel from the exploding cars sparked a small fire in one of the storage tanks, but it was quickly put out, it added.

At 5:50 a.m., security guards at a refinery in Mareb blew up two white cars loaded with explosives. The vehicles were similar to those driven by staff at the facility.

"They were driven by other suicide bomber terrorists who tried to break into (the facility)," the statement said.

The two attackers were killed and no one else was hurt in that attack, it said.

Saleh faces four opponents in Wednesday's elections — already marred by the abduction Sunday of four French tourists by tribesmen. The most serious challenger is Faisal bin Shamlan, who was chosen by five opposition parties as their candidate.

After the Sept. 11, 2001 attacks, Yemen allied itself with the United States and cracked down on militants.

But February's escape of the Al Qaeda militants raised questions about whether the country was a serious anti-terror ally. One of the fugitives had been convicted in the Cole and the Limburg bombings.

Click Here to Visit FOXNew.com's Mideast center.