Rumsfeld gave the assurance on Wednesday when he met Pakistani President Pervez Musharraf on a swift stopover during a tour that has taken him to Iraq and Afghanistan, spokesman Jalil Abbas Jilani said on Thursday.
Pakistan recently was rewarded by the US for its support of Washington's "war on terror" with an offer to sell Islamabad F-16 fighter jets in addition to a separate $1.3 billion arms package announced last year.
According to Jilani, Rumsfeld told Musharraf that the US would be "stepping up support to meet legitimate defence needs of Pakistan".
Peace and security
A Foreign Ministry statement quoted Musharraf as telling Rumsfeld the offer to sell the F-16s would be "an important factor for preserving regional peace and security".
Washington has offered fighter
jets to both India and Pakistan
Despite efforts over the past year by nuclear rivals Pakistan and India to bury five decades of enmity that has led to three wars, both countries are eager to upgrade their weaponry.
India has warned that delivering the F-16s to its neighbour could upset the fragile peace talks, and Pakistan has made similar complaints about India's ambitions to boost its own defence capability.
Washington appears to have balanced their demands by offering sophisticated fighter jets to both countries.
A Pakistani defence official said Musharraf and Rumsfeld shared views on US-led coalition operations against Taliban rebels in Afghanistan, and Pakistan's "successes" against al-Qaida-linked fighters in its tribal regions of North and South Waziristan since late 2003.
Central Asia stop
Rumsfeld arrived in Kyrgyzstan on Thursday for talks with the former Soviet state's new leaders, the first visit by a senior Western official since a coup on 24 March.
The Afghan government is still
heavily dependent on US help
The impoverished Central Asian state's interim government is trying to shore up stability since the ouster of president Askar Akayev, who ruled for nearly 15 years and fled after violent protests over a flawed parliamentary election.
Rumsfeld, who landed at the US Air Force's Ganci Air Base, was to meet acting President Kurmanbek Bakiyev and Foreign Minister Roza Otunbayeva, both key leaders in the protests that led to Akayev's ouster.
Bakiyev's interim government has pledged to allow the US to keep leasing the Ganci Air Base.
The base next to Bishkek's international airport is used to deliver supplies to Afghanistan.
Rumsfeld was to speak to US military personnel at the air base.
Russia also leases a military air base near Bishkek, making Kyrgyzstan the only country where both Russia and the US have established bases.
Rumsfeld (L) left open the issue
of permanent US military bases
During Rumsfeld's visit to Afghanistan on Wednesday, President Hamid Karzai said he was seeking a long-term security partnership that might keep US troops there indefinitely.
Karzai made the statement at a news conference with Rumsfeld, who was reluctant to discuss the Bush administration's level of interest in giving Afghanistan security guarantees.
It is not clear whether Rumsfeld would favour a long-term military presence in Afghanistan.
Some think he would prefer a more flexible arrangement for US aircraft overflight rights and possibly access to an Afghan air base for occasional training, refuelling and other activities.
The Pentagon has made such arrangements with other Central Asian nations.