WASHINGTON, Dec 2: The United States is urging Afghan President Hamid Karzai to sign a bilateral security agreement for keeping US troops in Afghanistan, during a Nato conference which begins in Brussels on Tuesday.

President Karzai’s refusal to sign the proposed pact has soured relations between the two allied nations and on Monday Afghan officials blamed US and coalition forces of deliberately withholding fuel supplies from Afghan army and police units.

US ambassador to Nato Douglas Lute told reporters on Monday that signing the agreement now would help unblock billions of dollars in US aid for Afghanistan after 2014, when the United States plans to withdraw most of its combat troops from the country.

The US media reported on Monday that the United States would like Afghanistan to sign the security deal during the two-day Nato foreign ministers’ conference.

The US media also quoted Ambassador Lute as telling reporters that the security agreement would be an important “first link in the chain” that could ultimately bring more than $8 billion for Afghan security forces and development assistance after Nato ends its combat mission at the end of 2014.

Last week, US National Security Adviser Susan Rice told a similar briefing that if President Karzai did not sign the proposed agreement by the end of this month, the United States would prepare for 100 per cent withdrawal from the country in 2014.

Ms Rice met President Karzai in Kabul last week but failed to persuade him to sign the bilateral agreement.

Mr Karzai further strengthened his position after a US drone strike killed a child and injured two women on Nov. 28 in Afghanistan’s Helmand province. “As long as unilateral acts and atrocities continue by American forces on our people, we won’t sign this BSA,” he said.

Earlier this month, a grand assembly of Afghan tribal elders known as the Loya Jirga, not only approved the agreement but also urged President Karzai to sign it immediately. Jirga leaders, including Mr Karzai’s political mentor Sibghatullah Mojaddedi, warned that without an agreement the Americans would not keep their troops in Afghanistan and Afghan defence forces were not yet ready to combat militants without external support.

Mr Karzai, however, said he was not in a position to sign the deal as he believed it should be signed by the new president elected after the general elections scheduled in April next year.