By Jibran Ahmad

ISLAMABAD (Reuters) - A delegation from the Taliban's political office visited Pakistan over the weekend, senior officials said on Saturday, for discussions that could include the latest informal effort to restart talks to end Afghanistan's long war.

The visit comes days after Taliban sources said they had held informal meetings with Afghan and U.S. officials in Qatar, the first direct meetings in more than a year after a fledgling process to halt the 15-year-old conflict collapsed.

Taliban sources said Mullah Abdul Manan - brother of the late Taliban founder Mullah Omar - met with U.S. and Afghan officials but there was no breakthrough toward restarting formal talks.

The Taliban delegation will brief Pakistani security agencies on the Qatar meetings - which did not include Pakistani representatives - and complain about the recent arrests of some of its senior commanders in Pakistan, a senior member based in Doha said.

Political office representatives Shahabuddin Dilawar, Jan Mohammad and Abdul Salam Hanafi traveled from Qatar and some other joined them in Pakistan, the official said.

Another Taliban member based in Afghanistan said the delegation had held one round of talks and would stay for few more days.

Taliban spokesman Zabihullah Mujahid confirmed a delegation was visiting Pakistan but would not comment on the Qatar talks, which he has denied took place.

"The delegation was sent to discuss some major issues with Pakistani leadership including the arrests of Afghan refugees and their repatriation to Afghanistan," Mujahid said.

Pakistan's Foreign Ministry spokesman said he had no information about any Taliban visit.

The Doha-based Taliban official said Pakistan was taken into confidence about the Qatar meetings, but they now believe Pakistan recently arrested some senior Taliban commanders to senior commanders to show their displeasure at being left out.

Another Taliban member said a few days ago Pakistani security agencies had raided a madrassa in Quetta and arrested another Taliban commander, Mullah Abdul Samad Sani.

"We don't know what's going on but this is second time during the past two months that Pakistani authorities raided a madrassa in Quetta to arrest senior Taliban member," the Quetta-based Taliban said.

Pakistan hosted the first and only round of official peace negotiations between the Afghan government and the Taliban insurgents to end a war that kills and maims thousands annually.

A planned second round of talks was called off after news broke that founder Mullah Omar had been dead for more than two years, sending the insurgent leadership into turmoil.

(Writing by Kay Johnson)