PESHAWAR, Pakistan — Truckers who carry supplies to NATO troops in Afghanistan have gone on strike in northwest Pakistan to protest lower pay, inadequate security and corrupt officials who demand bribes from the truckers, officials said Wednesday.

The supply route is an important lifeline for international forces in landlocked Afghanistan. The coalition ships a significant portion of its nonlethal supplies through Pakistan into southern Afghanistan. The other land route into Afghanistan through Central Asia and Russia is longer and more expensive.

The strike began in response to the government’s decision to require truckers to go through authorized companies to carry NATO supplies instead of making individual deals with the government-run National Logistics Cell, said Jehanzeb Khan, head of a transport workers union in northwest Pakistan. The companies pay the truckers less, said Khan.

He also claimed the government was not providing adequate protection to the drivers from Taliban attacks, and each truck had to pay corrupt security officials about $165 in bribes to pass through the Khyber tribal area on the way to the border.

Khan said truckers in northwest Pakistan stopped carrying NATO supplies Wednesday, and he was reaching out to others throughout the country to get them to join the strike.

Haneef Khan Marwat, head of a transportation company in the southern city of Karachi, said some truckers began their strike as early as last Friday and thousands of vehicles are involved. He said the strike would continue until the government reversed its new policy.

No trucks carrying NATO supplies crossed the northwest Torkham border Wednesday, said local political official Tahir Khan.

Torkham is one of two crossings used to ship NATO supplies to Afghanistan.

Goods continued to move through the other crossing, Chaman, in southwest Pakistan, said clearing agent Mohammed Asghar.

Pakistan closed its Afghan border to NATO supplies for seven months in response to U.S. airstrikes that accidentally killed 24 Pakistani soldiersin November 2011. Pakistan finally reopened the route after the U.S. apologized for the deaths.

Also Wednesday, police said they arrested five Pakistani Taliban militants involved in the killing of two female polio workers in the southern city of Karachi in December. Senior police official Ghulam Shabbir Shaikh told reporters that the five militants are from the northwest Swat Valley and confessed to their participation in the killings, saying they believed the polio vaccine was meant to make Muslim children sterile.

Nine people working on an polio-vaccination campaign were shot and killed in Pakistan last month, five of them in Karachi and four in the country’s northwest.

The Taliban have denied responsibility for the killings. But Islamist militants in Pakistan have opposed the vaccination campaign, claiming the health workers are spies and the vaccine would make children sterile.

Taliban commanders in Pakistan’s troubled northwest tribal regions also said last year that vaccinations can’t go forward until the U.S. stops drone strikes in the country.

Pakistan is one of three countries in the world where polio is still endemic.

Information for this article was contributed by Adil Jawad and Matiullah Achakzai of The Associated Press.

Front Section, Pages 5 on 01/10/2013