The United States announced on Thursday (Jan 4) it was suspending at least US$900 million in security assistance to Pakistan, in another sign of its dissatisfaction with what it says is Pakistan's failure to crack down on militant networks operating there.

Washington believes that Pakistan is not doing enough or turning a blind eye to groups such as the Afghan Taleban and the Haqqani network who have long launched attacks in neighbouring Afghanistan that led to the deaths of US troops using safe havens along the countries' border.

Pakistani leaders deny those claims, saying that militants in Afghanistan launch cross-border attacks of their own. They also argue that the US has refused to recognise their efforts to curb the militant groups.

Here is a closer look at the two militant groups involved in the US-Pakistan spat.

AFGHAN TALEBAN

The hardline group predominantly made up of ethnic Pashtuns - the largest ethnic group in Afghanistan - governed Afghanistan from 1996 until 2001, when it was toppled by a US-led invasion for harbouring the Al-Qaeda militant group and its leader Osama bin Laden.

The BBC reported that the group emerged in the early 1990s in northern Pakistan after the pull-out of Soviet troops following their occupation of Afghanistan.

According to the Council on Foreign Relations (CFR), the group sprung from an Afghan faction of Islamist guerrilla fighters who had been part of the Soviet resistance and were joined by young Pashtun tribesmen who had studied in Pakistani madrassas.

Although they first appeared at religious seminaries that preached a hard line form of Sunni Islam, they began to win popular support in the Pashtun areas between Pakistan and Afghanistan following the Soviet era by promising to restore peace and stability as well as imposing their stricter version of Syariah law when in power.

During Taleban rule, their harsh imposition of Islamic law and punishments - such as requiring women to wear the burka and public executions for adultery - became widely known around the world.

Although they were removed in 2001, the war dragged on and by 2003, the US had diverted its attention away to the Iraq war.

Headed by Mullah Mohammed Omar, the Taleban regrouped in their southern and eastern Afghanistan strongholds, from where they could easily cross into Pakistan's tribal areas. By 2009, they had become a formidable force with US intelligence officials acknowledging the effectiveness of their insurgency against the Western-backed goverment.

Although they have been diminished since US and Nato troops started withdrawing from Afghanistan in 2014, the Taleban has stepped up attacks across the country with Afghan security forces struggling to counter the resurgence.

Since May 2016, the group has been led by its new leader, Haibatullah Akhundzada, who has been described as a low-key but influential religious scholar.

Its mission, which initially stemmed from its resistance to foreign occupation, is now focused on challenging a government it considers a Western pawn.

The group is now still responsible for the majority of the attacks and casualties in the country.

As of August 2017, 13 per cent of the 407 districts in Afghanistan were under Taleban control or influence, according to a report by the Special Inspector General for Afghanistan Reconstruction.

Analysts say peace in Afghanistan will only come if the Taleban goes back to the negotiating table with the government, but while Pakistani officials have denied sheltering Taleban militants, talks and efforts to kick start negotiations have so far failed.

HAQQANI NETWORK

Designated by the US government as a terrorist organisation in 2012, the Pakistan-based Haqqani network is seen by Afghan officials and international terrorism authorities as one of the most lethal terror groups operating in the Afghan-Pakistani border region.

The group, which is affiliated with the Taleban, has been blamed for many high-profile attacks in Afghanistan, including a huge suicide blast in the Kabul diplomatic quarter in May 2017 that killed more than 150 people.

US officials have accused the group of being supported by elements of Pakistan's military and intelligence agency, with the aim of preventing its arch-rival India from extending its influence in the country - allegations that Islamabad have rejected.

The group is named after Jalaluddin Haqqani, who fought against Soviet forces in Afghanistan in the 1980s.

Born in 1939 in the Afghan province Paktia, he studied at Darul Uloom Haqqania, an Islamic seminary in the suburbs of Peshawar that is allegedly linked to Taleban and other extremist groups.

In 1996, a year after it became a component of the Taleban, the Haqqani helped it capture the Afghan capital of Kabul.

During Taleban rule, Jalaluddin was appointed minister of tribal affairs. He had reportedly maintained close links with then Taleban leader Mullah Mohammed Omar and former Al-Qaeda leader, Osama bin Laden.

Jalaluddin remained in his post until the fall of the Taleban in 2001. Since his death in 2015, his son Sirajuddin Haqqani has taken over and now also serves as the Taleban's deputy chief.

According to security experts, the group's base is in the city of Miranshah in Pakistan's North Waziristan region along the Afghan border.

While not much credible information is available on the younger Haqqani, he is believed to have grown up in Miranshah and studied at the same seminary as his father.

He is said to be an expert on military affairs and is more of a hardliner than his father.

Jalaluddin is believed to have had at least seven sons. Another of his son, Anas Haqqani, who was born to a woman from the United Arab Emirates is currently in Afghan custody and has been sentenced to death by a local court.

The Taleban has warned against his execution, saying there would be "disastrous consequences" if that happens.

SOURCES: BBC, AFP, CNN, AL JAZEERA, REUTERS, COUNCIL ON FOREIGN RELATIONS, VOICE OF AMERICA, DEUTSCHE WELLE