KABUL, Afghanistan â€"  Afghan security forces have arrested five militants with 10 metric tons (11 tons) of explosives that they had brought from Pakistan to use to carry out a massive attack in Kabul, as well as another three planning an assassination attempt against the vice president, an official said Saturday.

The reports of new planned attacks in the Afghan capital came a week after militants said to be part of a Pakistan-based group launched brazen coordinated assaults in the heart of Kabul and in other cities.

U.S. officials say they have stepped up pressure on Islamabad to crack down on that group, the Haqqani network, which specializes in high-profile strikes against well-protected targets.

Three of the five men arrested with the 10 tons were members of the Pakistani Taliban, while the other two belonged to the Afghan Taliban, National Director for Security spokesman Shafiqullah Tahiry said at a news conference. He said their orders came from militant leaders with ties to Pakistani intelligence. He did not say when the arrests took place, nor what their intended target was.

"Imagine if 10,000 kilograms of explosives, which was already inside Kabul" had exploded, "what a disaster could have happened," Tahiry said.

Tahiry said the captured explosives were in 400 bags and hidden under potatoes loaded in a truck with Pakistani license plates.

According to Tahiry, the men confessed that they "had planned to carry out a terrorist attack in a key point in Kabul city."

He claimed that the three Pakistani members of the group picked up the explosives just outside the Pakistani city of Peshawar, and were under the orders of two local Taliban leaders named Noor Afzal and Mohammad Omar, who Tahiry said had ties with the country's Inter-Services Intelligence agency, or ISI.

Tahiry also said that security forces had foiled a Haqqani network assassination attempt against Afghan Vice President Mohammed Karim Khalili.

He said three Afghan men arrested on April 15, the day the Kabul attacks began, planned to kill Khalili at his home. They were equipped with suicide vests and small arms.

According to Tahiry, the order to kill Khalili was issued in Miram Shah by Haqqani network commander Badruddin Haqqani. Last May, the U.S. designated Badruddin Haqqani a terrorist. He's the son of the group's founder, Jalaluddin Haqqani.

Afghan officials often blame Pakistan and the ISI for supporting militant groups -- including the Haqqani network -- in the country's lawless areas along the Afghan border. The Pakistani government has vehemently denied any such claims.

Last Sunday's coordinated assaults included near-simultaneous attacks in the three parts of the capital and three other eastern cities. Eight policemen and three civilians were killed in 18 hours of fighting, along with 36 militants, according to Afghan officials.

On Thursday the U.S. ambassador to Afghanistan said that there was "no question" that the Haqqani network was behind that attack and said Pakistan needed to do more to clamp down on the group's safe havens.

The comments were the strongest yet from a U.S. official blaming that incident on the Haqqani network.

"There is no question in our mind that the Haqqanis were responsible for these attacks," U.S. Ambassador Ryan Crocker told reporters in Kabul at the time. "We know where their leadership lives and we know where these plans are made. They're not made in Afghanistan. They're made in Miram Shah, which is in North Waziristan, which is in Pakistan."

"We are pressing the Pakistanis very hard on this," Crocker said.

Washington has long demanded that Pakistan target the Haqqani network. They are seen as more ideologically tied to Al Qaeda than some of the other militant groups, and they have been particularly adept at sophisticated strikes like the one this week. The group was also blamed for a similar attack in September in which militants took over a half-constructed high-rise in the capital and opened fire on the nearby NATO headquarters and U.S. Embassy with heavy weapons.