Washington  - The situation in Afghanistan is deteriorating and the country's Taliban and al-Qaeda insurgency are gaining strength, the top US commander for the region warned Wednesday as the US prepares to send thousands more troops to Afghanistan.

General David Petraeus, head of US Central Command, said in congressional testimony that insurgents had expanded their control over the southern and eastern parts of the country but vowed they would be fought "aggressively and relentlessly" by US forces.

Their success was being fuelled by drug money, the ability of insurgents to move freely across the Afghan-Pakistan border and growing public anger with the inability of the Afghan government to improve the lot of its people.

Taliban insurgents operating on the Pakistani side of the border were also posing "an ever more serious threat to Pakistan's very existence," Petraeus said, defending US aid to the Pakistani government and US air strikes along the border.

"The Taliban and other insurgent groups are growing in strength and waging an increasingly violent campaign against coalition forces and the Afghan state," Petraeus told the Senate's Armed Services Committee.

"Reversing the cycle of violence, defeating the extremist insurgencies in these countries, and eliminating safe havens for al- Qaeda and other trans-national extremist organizations require a sustained, substantial commitment," he said.

Obama on Friday laid out a new strategy for Afghanistan, the result of a two-month long review of US policy, vowing to dismantle al-Qaeda's operations in the region. The administration is sending an extra 21,000 troops and Obama also promised more civilian and diplomatic personnel to aid Afghanistan's economic recovery.

Some senators expressed scepticism over the US' new strategy in the region. Senator Carl Levin, a Democrat who chairs the Armed Services Committee, called for clear "benchmarks to measure progress" in Afghanistan.

Petraeus, who is credited with restoring a measure of stability in Iraq over the last year, echoed Obama's view that reducing the violence in Afghanistan would require a "much more robust" civilian response to complement the military's efforts.

Strengthening the Afghan government in many cases requires "building, not rebuilding" its institutions, Petraeus said. A key sign of success would be when Afghanistan's forces can take greater responsibility for their own security.

Petraeus also blasted Iran for supporting insurgents in both Afghanistan and Iraq as President Barack Obama has sought to engage the Islamic regime to help stabilize the region.

"The Iranian regime has also attempted to thwart US and international efforts to bring stability to Iraq and Afghanistan," he said.

US Secretary of State Hillary Rodham Clinton said US and Iranian officials met on the sidelines of a conference on Afghanistan in The Hague on Tuesday, though Iran has denied the exchange took place. The two countries have no formal relations.

Obama's troop increase will take the US presence in Afghanistan to more than 50,000 soldiers. The US president is also expected to push European countries to scale up their own troop contributions during a summit of NATO members in France and Germany later this week. (dpa)