KABUL, Afghanistan - The spring fighting season in Afghanistan geared up this weekend with a war of words.

The Taliban announced they will begin their spring offensive Sunday, pledging to attack military bases, convoys and Afghan officials, including members of the peace council working to reconcile with top insurgent leaders. Saturday's declaration came a day after a new Pentagon report claimed the militants were experiencing low morale after suffering heavy losses on the battlefield.

"The war in our country will not come to an end unless and until the foreign invading forces pull out of Afghanistan," the Taliban said in a two-page statement released by the leadership council of the Islamic Emirate of Afghanistan, which is what the movement calls itself.

Senior officers with the U.S.-led coalition said Friday that the Taliban - aided by the al-Qaida-linked Haqqani network - have plans to conduct a brief series of high-profile attacks, including suicide bombings, across the country in a display of power. The officers spoke on condition of anonymity to discuss recent intelligence, firmed up in the past couple days, that lead to the assessment.

Lt. Col. John Dorrian, a spokesman for the coalition, said the Taliban planned to use the violence as a "propaganda ploy" to try to demonstrate their relevance and create the perception of momentum despite recent setbacks.

In recent months, the U.S.-led coalition said it has seized insurgent weapons caches, pushed the Taliban from their historic strongholds in the south, and captured and killed hundreds of their fighters and field commanders. The Taliban have responded with suicide bombings and targeted attacks on Afghan and coalition troops and Afghan government officials.

In Brussels, a NATO official said Saturday that international forces had already tightened security in anticipation of an uptick in assassinations and spectacular attacks by the Taliban, who are claiming that they have infiltrated the ranks of the Afghan security forces. The official could not be identified in line with standing regulations at the alliance.

Security agencies employed by Westerners working in Afghanistan have issued lockdowns and travel restrictions. The Afghan intelligence agency said the government had tightened security. Defense Ministry spokesman Gen. Mohammad Zahir Azimi, who also described the Taliban statement as "propaganda," said the peace process was advancing and that the Afghan security forces with the cooperation of international forces were in a strong defensive position to counter the expected acceleration in violence.

The Pentagon report claimed coalition and Afghan forces had halted the insurgents' momentum in much of the country and reversed it in some important areas.

"The coalition's efforts have wrested major safe havens from the insurgents control, disrupted their leadership networks and removed many of the weapons caches and tactical supplies they left behind at the end of the previous fighting season," the report said.

However, the report also said that progress in development and in expanding the Afghan government's influence and control outside Kabul had not kept pace with security gains. Progress across Afghanistan remained "fragile and reversible" but the momentum generated in the past six months has provided the conditions for Afghan security forces to start taking the lead in security in seven areas beginning in July, the report said.

The Taliban, known for their resiliency, have conducted a number of brazen attacks in recent weeks.

This month, insurgents have launched deadly attacks inside the Afghan Defense Ministry, the police headquarters for the city of Kandahar in the south and at an Afghan-U.S. base in the east. The Taliban also tunneled into the Kandahar city jail and spirited out more than 480 inmates - most of them insurgents.

In announcing their spring offensive, the Taliban said insurgents would target "foreign invading forces, members of their spy networks and other spies, high-ranking officials of the Kabul puppet administration ... and heads of foreign and local companies working for the enemy and contractors."

The Taliban ordered its fighters to pay "strict attention" to protecting civilians during the spring offensive. A recent U.N. report said about three-quarters of the estimated 2,777 civilians killed in Afghanistan last year died at the hands of insurgents, not international forces.