Beirut, Lebanon ? Under intense pressure to cooperate with a U.N. probe, Syria on Saturday invited the chief U.N. envoy investigating the assassination of former Lebanese Premier Rafik Hariri to visit Damascus and meet with Syrian authorities.

But in a move sure to turn the heat up against Syria, a Lebanese judge accused four pro-Syrian Lebanese generals of carrying out the Feb. 14 Beirut bombing that killed Hariri and 20 others. The judge ordered the generals be held in police custody until a trial begins to hear the official charges against them.

The generals ran this country’s pro-Syrian security forces when Hariri was killed and were taken in for questioning Tuesday after a top United Nations investigator alleged they may have played a role in Hariri’s murder.

A fifth Lebanese suspect identified by the U.N. team, former pro-Syrian lawmaker Nasser Qandil, was questioned and released.

Despite denials by Syria and its Lebanese allies of any involvement in the killing, Damascus has been accused of failing to cooperate with a U.N. investigation team led by German prosecutor Detlev Mehlis, who has said he is willing to meet Syrian officials in their country.

But in a terse statement released by its state-run news agency, Syria on Saturday invited Mehlis to visit Damascus and meet Syrian officials on Monday or Tuesday, although it was not immediately clear which officials he would meet.

A Syrian Foreign Ministry official, speaking on condition of anonymity because he was not authorized to speak to the media, said Mehlis was unavailable on either of those days and would visit on Sept. 10 instead.

Faisal Mekdad, Syria’s ambassador to the United Nations, invited Mehlis “in the framework of Syria’s readiness to cooperate with the international investigation.”

“Mr. Mehlis is welcome in Damascus,” Mekdad told Al-Arabiya TV by telephone from New York, adding that his country “has an interest in this investigation in order to eliminate all allegations and to prove that Syria has nothing to do at all with this case.”

The arrest warrants against the four generals – among Lebanon’s most powerful figures during Syria’s three-decade control over Lebanon – were issued by Elias Eid, the Lebanese investigating magistrate who spent two days questioning them.

Eid accused the generals of “deliberate killings, participation in the planning, execution and bombing that led to the killing (of Hariri and 20 others) …, carrying out terrorist acts and possession of arms and explosives,” according to a senior court official who revealed the contents of the warrants to The Associated Press.

If officially charged on the basis of the accusations, the generals will face counts that carry the death penalty, said the official who spoke on condition of anonymity as he was unauthorized to speak to the media. Lebanese Prosecutor-General Said Mirza has issued preliminary criminal charges against the four generals.

The suspects are Brig. Gen., Mustafa Hamdan, current commander of the Presidential Guards; former General Security chief Maj. Gen. Jamil Sayyed; ex-director general of Internal Security Forces, Maj. Gen. Ali Hajj; and Brig. Gen. Raymond Azar, the former director general of military intelligence.