Militants on Saturday threatened more attacks on tankers carrying fuel to Afghanistan through Pakistani routes to avenge the incursions, after setting fire to three dozen of the vehicles.
"Unless the reaction cools down and we make sure that the supply line is secured, we cannot reopen it," Foreign Ministry spokesman Abdul Basit said.
"It's just because of security reasons. There's no timeframe. I think it should be done soon."
Angered by repeated incursions by Nato helicopters over the past week, Pakistan blocked a supply route for Nato troops in Afghanistan after one such strike killed three Pakistani soldiers on Thursday in the northwestern Kurram region.
The Nato incursions and the closing of the supply route, now in its fourth day, have heightened tensions between the United States and Pakistan, whose long alliance is often uneasy.
A joint Pakistani and Nato investigation of the incident has started, said a Pakistani military official.
"In such a situation, allowing these trucks to carry on with their journey would be inviting more attacks so there's no need to rush," said the official.
Civilian casualties caused by the missile-carrying pilotless drones, operated by the US Central Intelligence Agency, have infuriated many Pakistanis and made it harder for the government to cooperate with the United States.
The CIA has escalated drone strikes against al Qaeda-linked militants in Pakistan's northwest, with 21 attacks in September alone, the highest number in a single month on record.
Two more drone strikes on Saturday killed 18 militants, Pakistani intelligence officials said. As is often the case, there was no independent verification of the attack. Taliban militants almost always dispute official death tolls.
A plot to stage coordinated attacks in Europe was disrupted in its early stages by drone strikes against militants in Pakistan, but it was not clear if the threat was fully erased, security sources said earlier in the week.
The alleged plan again put the spotlight on Islamabad, which is under US pressure to crack down harder on militans who operate out of sanctuaries in Pakistan and cross into Afghanistan to attack Western troops.
The latest strains in US-Pakistani relations come during domestic turmoil. Pakistan is reeling from floods which have made over 10 million people homeless, caused billions of dollars in damages and hurt the agriculture industry, the economy's mainstay.
The government may be headed for another showdown with the judiciary, and media speculation is swirling that the military may try to manipulate politics to avoid instability, after Pakistani leaders' perceived mishandling of the floods.
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