The Taliban declared the start of a spring offensive across Afghanistan on Saturday, warning they would target foreign troops, as well as Afghan security forces and top government officials, in a wave of attacks including suicide bombings.

In a statement, the hardline Islamists warned Afghan civilians to stay away from public gatherings, military bases and convoys, as well as Afghan government centres and buildings, as these would be the focus of attacks starting on May 1.

The Taliban statement comes just a day after senior military officials and Western diplomats warned they expected a surge in insurgent attacks over the next week, beginning on Sunday.

"The Leadership Council of the Islamic Emirate of Afghanistan wants to declare the launching of the spring military operations named as "Badar" to be waged against the invading Americans and their foreign allies and internal supports," the Taliban said in an emailed statement.

"Operations will focus on attacks against military centres, places of gatherings, airbases, ammunition and logistical military convoys of the foreign invaders in all parts of the country," the Taliban said.

Senior military officials told Reuters on Friday that recent intelligence reporting indicated the campaign of increased violence would last about a week and would be mounted by the Taliban, supported by the al Qaeda-linked Haqqani network and other insurgents.

Washington and commanders of the NATO-led International Security Assistance Force (ISAF) have trumpeted successes against a growing insurgency since 30,000 extra U.S. troops were sent to Afghanistan last year.

Civilian Warning

The Taliban said the targets of the attacks would be foreign forces, high-ranking officials of President Hamid Karzai's government, members of the cabinet and lawmakers, as well as the heads of foreign and local companies working for the NATO-led coalition.

"All Afghan people should bear in mind to keep away from gatherings, convoys and centres of the enemy so that they will not become harmed during attacks of Mujahideen against the enemy," the Taliban said.

Senior military commanders have long anticipated a spike in violence with the arrival of the spring and summer "fighting season", although the usual winter lull was not seen as U.S-led forces pressed their attacks against insurgents, particularly in the Taliban's southern heartland.

Violence across Afghanistan hit record levels in 2010, with civilian and military casualties the worst since U.S-backed Afghan forces toppled the Taliban government in late 2001.

The Pentagon said in a biannual report on Friday that an overall increase in violence was due in part to increased targeting of safe insurgent safe havens and unseasonably mild winter weather.

Earlier this month a suicide bomber wearing a police uniform killed Gen. Khan Mohammed Mujahid, the Kandahar police chief, while another uniformed suicide bomber killed five NATO soldiers. An Afghan pilot shot dead eight U.S. soldiers and a civilian contractor at Kabul airport this week.

The Taliban did not say how long their stepped-up campaign would last, but said it had been codenamed "Badar" after a decisive Muslim 7th Century battle victory in western Arabia that Muslims attribute to divine intervention.

In the statement, the Taliban repeated their frequent claim that fighting in Afghanistan would not end until foreign troops had left the country. They also called on Afghan government officials and security forces to switch sides to the insurgency.

Military commanders interviewed by Reuters this week were not sure why May 1 had been chosen by the Taliban to launch their renewed offensive.

The anticipated Taliban campaign would not change the coalition's counterinsurgency strategy put in place last year by U.S General David Petraeus, the commander of the 150,000 U.S. and ISAF troops in Afghanistan, they said.

Under a programme agreed at a NATO summit last year, ISAF said it will begin handing security responsibility to Afghan forces in several areas from July. The programme will end with the withdrawal of all foreign combat troops by the end of 2014.