America has signalled a radical new initiative to bring the Taliban into the Afghan political process as part of growing efforts to achieve a peaceful resolution to the war in Afghanistan.

The US ambassador to Kabul told the Observer that America would be prepared to discuss the establishment of a political party, or even election candidates representing the Taliban, as part of a political strategy that would sit alongside reinforced military efforts to end the increasingly intractable conflict.

The move will cause concern among allies struggling to keep pace with rapidly evolving US policy.

Other ideas being discussed include changing the Afghan constitution as part of potential negotiations, taking senior Taliban figures off UN blacklists to establish dialogue and possible prisoner releases.

European nations are currently weighing up US requests for more troops and resources for Afghanistan ahead of a series of forthcoming summits. Tough fighting is expected as America sends a surge of 17,000 troops into the country before the August elections. In recent days more than 100, including five Nato soldiers, have died in fighting and bomb attacks across the country. More than 30 insurgents died in a clash in the southern Helmand province, a Nato spokesman said.

William Wood, the outgoing US ambassador to Afghanistan, told the Observer that "insurgencies, like all wars... end when there is an agreement". He said while the US saw "no way there could be power-sharing or an enclave" for the Taliban, "there is room for discussion on the formation of political parties [or] running... for elections. That is very different from shooting your way into power." The key requirement would be respect for the constitution, Wood added.

"They have said 'No start of negotiations without prior departure of foreign forces.' That's not serious. Let's get serious."

Taliban and other insurgents are currently flowing into Afghanistan from Pakistan as milder weather allows passage over the mountains.

Last week, the head of Nato forces in Afghanistan, General David McKiernan, admitted to the Observer that his troops "were not winning" in the south and parts of the east of the country, though progress was being made elsewhere. This year will be "critical" and "tough", he said.

In Kabul, the Observer has discovered at least four attempts at exploratory negotiations between insurgents, their representatives and the Afghan government. One involves Gulbuddin Hekmatyar, the Islamist warlord and former prime minister, whose militants are responsible for the deaths of hundreds of international and Afghan soldiers and civilians in the east of Afghanistan. Two weeks ago Hekmatyar's representatives and government emissaries met in a hotel in Dubai, according to Senator Arsala Rahmani, a former Taliban minister who is a key intermediary. Rahmani also claims to have been in touch with Jalaluddin Haqqani, a veteran militant behind a series of bloody attacks in Kabul and eastern Afghanistan.

Other contacts include those between Taliban leaders and President Hamid Karzai's brother, and those brokered by a group of ex-Taliban leaders now living under amnesty in Kabul including Abdul Salam Zaeef, former ambassador to Pakistan. Nato and EU officials have met Zaeef to discuss Taliban demands. A Pakistan-Afghan "jirga", or assembly of elders, has established a "reconciliation committee" to "reach out to extremists".

Meanwhile, Prime Minister Gordon Brown is to launch a new British counterterrorism strategy targeting Pakistan. Writing in today's Observer he warns of an "al-Qaida core in northern Pakistan trying to organise attacks in Britain".

Al-Qaida is still active in Afghanistan but the threat has crossed the border, he adds: "Over two thirds of the plots threatening the UK are linked to Pakistan. Together with the US administration we are developing a new strategy for how we tackle the terrorist threat across the region, the underlying causes, the extremist madrasas and the lawless spaces in which terrorists can recruit or train."

Writing after British Muslim cleric Anjem Choudary suggested homosexuals be stoned, Brown also urged civic society "to stand up to people who advocate violence and preach hate" and promised a new approach to threats of chemical, biological and nuclear attack.

In Kabul, Wood said the upper ranks of the Afghan insurgency had yet to show any "inclination" for reconciliation. Al-Qaida remained "the enemy of the world", making talks inconceivable.

