The Spanish government named a Moroccan extremist group linked to Al Qaeda (search) as the main focus of the Madrid bombing probe and said Tuesday that investigators were making swift progress.

The Moroccan Islamic Combatant Group (search), forerunner of a group blamed for last year's homicide bombings in Casablanca, is now the "priority," Interior Minister Angel Acebes said -- a reversal of the government's initial statements that the prime suspects were Basque separatists (search).

"Other options are not being ruled out, but primarily the investigation is going to go in this direction," Acebes told reporters.

The group had surfaced in Spanish news reports, but this was the first time a Spanish government official publicly identified it as the focus of investigation into the March 11 commuter train bombings (search).

Acebes said witness testimony and the discovery of a rural house where the attackers were believed to have assembled the backpack bombs used in the attacks have led investigators closer to unraveling the plot behind the bombings, which killed 191 people and wounded more than 1,800.

"The investigation is advancing. In 18 days we have arrested 23 people including some of the chief perpetrators of the attack," Acebes said. Moroccan, British and German authorities were involved in the investigation, he added.

Court officials said Judge Juan del Olmo would issue an international arrest warrant for five other suspects Tuesday.

The Spanish news agency Efe said Abdelkrim Mejjati, a 36-year-old Moroccan reportedly believed to have masterminded the attack, was among the five being sought. Court officials would not confirm the report.

Moroccan authorities have said Mejjati was linked to the homicide bombings in Casablanca last May, but that his role in the Madrid attack was unclear. He is also wanted by the FBI in connection with possible terrorist threats against the United States.

Of those arrested, 18 people remain in custody -- 11 Moroccans or Moroccan-born Spaniards, two Indians, two Spaniards and three Syrians.

Fourteen of the suspects have been charged with mass murder or collaborating with or belonging to a terrorist group.

Four more have yet to go before a judge. They are a Moroccan arrested Friday, two Syrians arrested Tuesday and Antonio Toro Castro, the brother-in-law of a Spaniard charged with supplying dynamite to the bombers. Court officials identified the Syrians as Walid Altaraki and Mohamad Badr Ddin Akkad.

At least six witnesses, including some who were wounded in the attack, identified prime suspect Jamal Zougam and two other suspects in a lineup on Friday, according to Spanish media reports.

Witnesses said they saw Zougam leave a backpack before stepping off one of the four trains that were bombed, radio station Cadena Ser reported.

Zougam was arrested with his half-brother, Mohamed Chaoui, two days after the attack.

Their mother, Aicha Achab, told the newspaper El Mundo that Zougam and Chaoui were innocent and that they were in her Madrid apartment when the attack happened. "I was preparing breakfast, like every morning, and we saw what happened on television," Achab was quoted as saying.

Moroccan investigators also have said another extremist group -- Salafia Jihadia -- was a focus of the probe. Salafia Jihadia was accused by the Moroccan government of organizing five near-simultaneous attacks in Casablanca that killed 45 people, including 12 homicide bombers.

The Moroccan Islamic Combatant Group is a forerunner to the Salafia Jihadia and is considered the first radical jihad movement in Morocco.

At least five members of the group, including leaders Nouredine Nfia and Salahedine Benyaich, trained in Al Qaeda camps in Afghanistan between 1999 and 2001, Moroccan officials said.

A report on terrorism issued by the U.S. State Department in 2002 said the group appeared to have emerged in the late 1990s. They interact with other North African extremist groups, especially in Europe, the report said, adding that members traffic falsified documents and possibly are involved in gunrunning.

The United States ordered the group's assets frozen in 2002.

In the immediate aftermath of the March 11 attacks, the government insisted the armed Basque separatist group ETA was its prime suspect, even as evidence emerged of an Islamic link. Acebes was among those accusing ETA, saying it "had been looking for a massacre" and "achieved its goal."

But in an interview published Monday in the newspaper ABC, Acebes said investigators had turned up no evidence of ETA involvement. "In the investigation, none," Acebes was quoted as saying.

Investigators have analyzed a videotape in which a man claiming to speak on behalf of Al Qaeda said the group carried out the Madrid attacks in reprisal for Spain's backing of the U.S.-led war in Iraq.