ISLAMABAD: US Secretary of State John Kerry is expected to meet Pakistan's Prime Minister Nawaz Sharif, outgoing President Asif Ali Zardari, Adviser on Foreign Affairs and National Security Sartaj Aziz and Chief of Army Staff Gen Ashfaq Parvez Kayani on Thursday.

Kerry flew into Pakistan on Wednesday night to hold meetings with the top political and military leadership aimed at easing tension over US drone strikes, the war in neighboring Afghanistan, and the fight against Islamic extremism.

The US secretary of state arrived in Islamabad shortly before 9pm (1600 GMT) on a trip that was not announced ahead of time because of security concerns.

Kerry plans a stop in London on his return to Washington.

“Our issues that we will discuss with the Pakistanis are counterterrorism, cross-border militancy, the economic agenda and how we can continue to partner in terms of promoting a secure and stable Afghanistan,” a senior US official told reporters travelling with Kerry.

Kerry is also expected to press the new Pakistani government on eliminating Islamist militant safe-havens as US-led troops prepare to leave Afghanistan.

“Safe havens for extremist groups clearly threaten our interests, our allies in the region and most of all Nawaz Sharif's own ability to execute his reform agenda and provide greater economic stability,” the senior official said.

Earlier on Wednesday, PM Sharif met with Chief of Army Staff General Ashfaq Pervez Kayani and discussed the agenda for their meetings with the US secretary of state.

It is Kerry's first visit to Pakistan as Secretary of State although he has visited the country in other capacities before and he is the most senior US official to visit the country since Nawaz Sharif was sworn in as Pakistan's new prime minister after May elections.

However, drone strikes are expected to be another point of contention.

Washington says it needs to attack dangerous militants with drones because Pakistan's government refuses to engage them militarily.

Pakistan contends the drone strikes are a fresh violation of its sovereignty, and they have increased widespread anti-American sentiment in the country.

The United States has reduced the number of drone attacks against militants in Pakistan and limited strikes to top targets. These moves appear to have appeased Pakistan's generals for now, US officials said.

But some officials are worry about pushback from the new civilian officials, including Sharif, who wants the attacks ended.

There have been 16 drone strikes taken place in Pakistan so far this year, compared with a peak of 122 in 2010, 73 in 2011 and 48 in 2012, according to the New America Foundation, a US-based think tank.

Meanwhile, as Washington's top diplomat John Kerry landed in Islamabad, the White House described the relationship with Pakistan as vitally important to US national security interests.

“Our relationship with Pakistan is extremely important to America's national security interests. It is a complicated but important relationship, as we've discussed in the past here,” White House spokesman Jay Carney said.

Carney also listed some of the subjects Kerry would be discussing with the top Pakistani leadership and noted that Pakistanis have been a big victim of terrorism.