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Rahmat Gul, Associated Press
Afghan security forces inspect the site of a suicide attack in Kabul, Afghanistan, Wednesday, Nov. 19, 2014. Four Taliban militants targeting a compound housing foreign workers in the Afghan capital were killed Wednesday night in a failed assault there, police said, the latest violence targeting foreigners in the country.

KABUL, Afghanistan — The Afghan capital has become a city under siege as the Taliban stage almost daily attacks against government and foreign targets, penetrating layers of heightened security and fueling concerns that insurgents have infiltrated the security forces.

Kabul is protected by a fortress-like "ring of steel," with police and soldiers manning roadblocks and spot-checking vehicles. Streets around important buildings such as parliament, ministries and the presidential palace are blocked off, while others are protected by razor wire and concrete blast walls.

But in recent weeks, insurgents have managed to attack two foreign compounds in Kabul, carry out a suicide bombing meters away from the office of the city's police chief, sent suicide bombers against international military bases and convoys, and bombed the car of a prominent female parliamentarian.

The police chief and the parliamentarian survived, but civilian casualties have been high.

This year the Taliban has shown particular strength across the country, with Afghan security forces suffering record-high casualties after taking the lead in the war from international forces in mid-2013. The Haqqani network -- which like the Taliban is based in neighboring Pakistan -- has also escalated attacks characterized by deployment of suicide bombers.

The decision by President Ashraf Ghani to sign a bilateral security agreement (BSA) with Washington immediately after his September inauguration has prompted the escalation in attacks, according to analysts, diplomats and the Taliban themselves.

The BSA, along with a Status of Forces agreement with NATO, will keep around 12,000 foreign troops in Afghanistan after the U.S. and NATO withdraw combat forces at the end of the year.

Waheed Mozhda, formerly a diplomat for the Taliban's 1996-2001 administration and now a political analyst, said: "This war will continue for years and years because of the BSA."

"There are a lot of people inside the government cooperating with the insurgents because they are opposed to the BSA," he said.

Attacks have become so frequent that First Deputy President Abdul Rashid Dostum turned up at the site of a suicide attack on a foreign compound on Tuesday to accuse forces within the Afghan government of collusion with insurgents.

He was expressing the concerns of many Kabul residents, who also accuse Pakistan of harboring the insurgents and using them as a means to preserve influence in Afghanistan after the Western combat mission ends.

"These attacks are part of an intelligence war with involvement of a foreign country," said Gen. Mohammad Zahir, Kabul's police chief, referring to Pakistan's ISI intelligence service. Zahir narrowly escaped an assassination attempt earlier this month when a suicide bomber detonated his payload in the heart of the city's heavily-guarded police headquarters in a major security breach.

The complexity of the attacks — with gunmen, suicide bombers, explosives and intricate planning to gain access to high-security installations and prominent people — was evidence of the backing of "foreign intelligence," he said.

Analyst Antonio Giustozzi said the attacks were "sending political messages to Ghani, the Americans, the expatriate community and probably to those members of the Taliban that might be interested in negotiating for peace."

The message, he said, is "this is jihad, we have to kick out the foreigners, the Americans, the crusaders and until that is achieved no compromise is possible."

Western diplomats and analysts have said Ghani's efforts to broker a peace deal with the Taliban, with support from Saudi Arabia, China and Pakistan, will be met with intensified insurgent activity for at least another two years as the Taliban test his resolve.

Mozhda, however, said "There is no door open for peace talks."

His warning was echoed by Taliban spokesman Zabihullah Mujahid, who described the BSA as "against the interests of the Afghan nation."

"The attacks in Kabul are aimed at breaking the backs of the foreign troops and the Afghan government; the fight will not stop," he said.