Washington, Nov 16 US President Barack Obama has written a letter to his Pakistani counterpart Asif Ali Zardari, asking him to step up the offensive against the Taliban and al Qaeda.

The New York Times reported on Sunday that the Obama Administration was leaning on Pakistan to step up its fight against the Taliban and al-Qaeda.

Obama's National Security Adviser General James L. Jones was sent to Islamabad with a letter for Zardari, The New York Times quoted sources, as saying.

"His (President Obama's) message, officials said, was that the new American strategy would work only if Pakistan broadened its fight beyond the militants attacking its cities and security forces and went after the groups that use havens in Pakistan for plotting and carrying out attacks against American troops in Afghanistan, as well as support networks for Al Qaeda," the paper reports.

In the letter, Obama said he expected Pakistan to do more to fight the extremists threatening Pakistan and Afghanistan.

"General Jones also delivered a letter from Obama to Zardari, in which Obama said he expected Zardari to rally the nation's political and national security institutions in a united campaign against extremists threatening Pakistan and Afghanistan," the NYT quoted an official, as saying.

Obama is expected to announce some troop increases in Afghanistan along with clearer limitations on US goals for the war after he returns from Asia late this week, the Dawn reports.

The announcement is expected either just before or just after the Thanks giving holiday on November 26. (ANI)