A deadly homicide bombing (search) at a mosque and an attempt to down a U.S. military aircraft with a shoulder-launched missile may signal the start of a campaign of violence by Al Qaeda (search) and Taliban rebels to destabilize Afghanistan's (search) legislative elections, President Hamid Karzai's spokesman said Tuesday.

Twenty people were killed in the June 1 blast in the southern city of Kandahar during the funeral of a moderate Muslim cleric who had spoken out against Taliban-led insurgents. Among the dead was the Kabul police chief and six of his bodyguards.

U.S. military spokesman Lt. Col. Jerry O'Hara confirmed that a shoulder-launched, surface-to-air missile was fired at U.S. aircraft on June 1. He said such attacks were infrequent and described it as an "isolated incident."

Ludin said the Afghan government believed the attacks "were in fact related" and "the aim was to create maximum effect ... maximum shock among the people."

"It's only logical to assume that the enemies of Afghanistan, the remnants of the Taliban, Al Qaeda elements with links to circles outside the country, would have chosen this time to obviously set a plot in motion," he said. "They may have gathered all their resources ... to be able to do this."

A recent surge in violence, after a lull during the bitter winter months, "may be related to the parliamentary elections" set for Sept. 18, Ludin said. He compared the assaults to bloodshed that preceded October's presidential elections.

At least 13 election workers were killed ahead of those polls.

Ludin said Afghan security forces were working closely with coalition and NATO-led international forces to safeguard the elections.

Ludin said the preliminary results of an investigation into the mosque bombing confirmed it was a homicide attack carried out by a foreigner and probably aimed at killing senior officials attending the funeral.

Kandahar Gov. Gul Agha Sherzai said last week the attacker was an Arab member of Osama bin Laden's terrorist network. He said an intelligence report indicated that Arab Al Qaeda teams had entered Afghanistan to carry out terror attacks.