WASHINGTON (Reuters) - The United States has not yet seen Pakistan take significant steps to clamp down on the Afghan Taliban and the Haqqani network militant groups, a senior U.S. administration official said on Friday.

The administration suspended about $2 billion in security assistance to Pakistan in January but Islamabad has failed to take “the kind of decisive and irreversible action” Washington has asked for to help with the war in Afghanistan, the official told reporters.

The administration has been frustrated by what it sees as Pakistan’s reluctance to act against the Afghan Taliban and the affiliated Haqqani network. Washington believes the groups use Pakistan as a safe haven for launching attacks on neighboring Afghanistan. Pakistan denies helping the militants.

The United States has been at war in Afghanistan since 2001, making it America’s longest military conflict. President Donald Trump agreed in August to a stepped-up military campaign against the Taliban, and has since increased pressure on Pakistan to help.

U.S. Defense Secretary Jim Mattis on Tuesday said he has seen some positive signs from Islamabad, including Pakistani military operations along the border - and the senior administration official agreed.

“I think the Pakistanis have wanted to appear responsive to our requests,” the senior administration official said, speaking on condition of anonymity.

“What I would say is, they have done the bare minimum to appear responsive to our requests,” the official said, saying more proactive steps were needed.

U.S. officials have told their Pakistani counterparts what types of actions are needed to lift the suspension of aid, the official said, declining to elaborate on the specifics.

“We are prepared to take steps that we think are necessary to safeguard U.S. personnel and interests in the region,” the official said, declining comment on what those steps would be, and on deadlines for action.

“We are continuing to look for real action, not just words, from Pakistan on the Taliban and Haqqani sanctuaries,” the official said.