ISLAMABAD — Thousands of followers of leading Islamist clerics began marching Sunday from the eastern city of Lahore to the capital, Islamabad, to protest Pakistan's decision to once again let NATO move Afghanistan-bound supply convoys through the country after a seven-month hiatus.

The protest was organized by the Defense of Pakistan Council, a coalition of hard-line religious groups that has among its leaders Hafiz Muhammad Saeed, an Islamic cleric who India claims engineered the 2008 terrorist attacks in Mumbai that killed 166 people.

Pakistani leaders have been bracing for a popular backlash since announcing last week that it was allowing NATO supply routes through the country to reopen after a blockade imposed when American airstrikes mistakenly killed two dozen Pakistani soldiers along the Afghan border in November. The first NATO container trucks crossed from Pakistan to Afghanistan on Thursday.

Until Sunday, protests against the resumption of NATO supply convoys have been relatively small and sporadic.

Though the Defense of Pakistan Council's popularity is largely confined to conservative followers, Pakistani officials are nevertheless watching the group's actions closely, mainly because anti-American sentiment runs high throughout the country. Some experts believe Pakistani civilian leaders delayed reopening the NATO supply routes for so long out of concern that the move would trigger anger against President Asif Ali Zardari's government as it prepares for national elections.

Along with Saeed, the Defense of Pakistan Council's leadership includes Maulana Samiul-Haq, regarded by many as the father of the Taliban movement, and Hamid Gul, a former chief of Pakistan's premier spy agency, Inter-Services Intelligence, who has long been viewed as a key supporter of insurgents battling U.S.-led coalition forces in Afghanistan.

Saeed, seen atop a vehicle leading the caravan Sunday, maintains a high profile despite the $10 million bounty that the U.S. government placed on him in April. He is suspected of having ties with al-Qaida and, with the help of the spy agency, founded the militant group Lashkar-e-Taiba in the 1980s.

Afghan blast kills

6 American troops

KABUL, Afghanistan — In what was an extraordinarily violent day even by Afghan standards, separate incidents on Sunday killed seven Western troops, including six Americans who died in a single blast, along with five Afghan police officers and at least 18 civilians, officials said.

The six Americans died in an explosion in eastern Afghanistan, where fighting has been on the increase. The North Atlantic Treaty Organization force confirmed the deaths late Sunday without disclosing the nationality of those killed, but a U.S. official said they were Americans.

The civilians, including women and children, were killed in three blasts along Afghanistan's border with Pakistan.

More than 225 NATO service members have been killed in Afghanistan this year.