Pakistan said as many Taliban groups as possible must be persuaded to join any upcoming peace discussions with the Afghan government, as a third round of four-country talks aimed at reviving negotiations with the insurgent group began Saturday.

Delegates from Afghanistan, Pakistan, China and the United States convened in the Pakistani capital Islamabad over the weekend even as the insurgents wage an unprecedented winter campaign of violence across Afghanistan.

Pakistan's advisor for foreign affairs Sartaj Aziz said a joint effort would help persuade the Taliban to join the process and lead to a "significant" reduction in violence.

"We believe our collective efforts at this stage, including through supportive CBMs (Confidence Building Measures), have to be aimed at persuading the maximum number of Taliban groups to join the peace talks," Aziz said during his opening statement at the third-round of talks on Saturday.

"In our view, a clear, well-defined and actionable roadmap for the peace process between the Afghan Government and Taliban groups is important."

The first round of the roadmap talks was held in Islamabad last month, where delegates began laying the groundwork for direct dialogue between Kabul and the Islamist group.

A second round was held in Kabul on January 18 which urged the Taliban groups to enter into early talks with the Afghan government without preconditions.

Taliban representatives have been notably absent during the process and analysts caution that any substantive talks are still a long way off.

The Taliban has stepped up attacks on government and foreign targets in Afghanistan this winter, when fighting usually abates, underscoring a worsening security situation.

Observers say the intensifying insurgency highlights a push by the militants to seize more territory in an attempt to wrangle greater concessions during talks.

Pakistan -- the Taliban's historic backers -- hosted a milestone first round of talks directly with the Taliban in July last year.

But the negotiations stalled when the insurgents belatedly confirmed the death of longtime leader Mullah Omar, sparking infighting within the group.

Afghanistan sees the support of Pakistan as vital to bring the Taliban to the negotiating table.