Violent attacks in Afghanistan's war jumped to record levels in the last quarter of 2019 while the strength of the country's embattled defense forces declined to its lowest level in four years, a U.S. government watchdog said Friday, as talks between Washington and the Taliban continue over the possible withdrawal of foreign troops.

Underscoring the conflict's continued toll despite a relative calm in Kabul, the latest quarterly report by the U.S. Special Inspector General for Afghanistan Reconstruction (SIGAR) noted that "enemy-initiated attacks" rose sharply last year, with the fourth quarter seeing a total of 8,204 attacks – up from 6,974 in the same period in 2018.

September, when the first round of presidential voting was held, saw the highest number of casualty-causing attacks since recording began in 2010.

SIGAR noted that attacks appeared to mirror progress in U.S.-Taliban talks, with incidents dropping earlier in the year, then picking up again after U.S. President Donald Trump temporarily halted negotiations in September.

"A turbulent last six months resulted in increases in overall enemy attacks (6 percent) and effective attacks (4 percent) in 2019 compared to the already high levels reported in 2018," SIGAR said in its quarterly report to the U.S. Congress.

The Pentagon has also continued to up the tempo of operations, with American warplanes dropping more bombs on Afghanistan in 2019 than at any other time in at least a decade, according to the U.S. Air Force.

Washington and the Taliban are continuing to wrangle over a possible agreement that would see U.S. troops begin to leave Afghanistan in return for security guarantees.

The U.S. has for months been calling on the militants to reduce violence, but both sides have said little in recent days about the status of talks and the Kabul government wants the U.S. to push for a full ceasefire.

The negotiations, due to resume in Qatar on February 25, are centered on a possible ceasefire and the withdrawal of thousands of U.S.-led NATO forces. Many obstacles remain before that would be possible but an eventual pullout would place the Afghan defense forces under even more pressure.

The SIGAR report noted that the control of Afghanistan's territory and population "became somewhat more contested (and) Afghan government control or influence continued to decline."

It put districts under government control or influence at 53.8 per cent covering 63.5 percent of the population by October 2018, with the rest of the country controlled or contested by the Taliban.

The hardline Islamist group has been unable to seize a major Afghan city but has stepped up pressure in rural areas and is now more powerful than any at other time since they were toppled by U.S.-backed Afghan forces in late 2001.

SIGAR cited a U.S. Forces-Afghanistan report that the Afghan National Defence and Security Forces had decreased to 308,693 troops, or 87.7 percent of its assigned strength, the lowest since the creation of NATO's operation to train, advise and assist Afghans in January 2015.

The U.S. has some 14,000 troops in Afghanistan as part of the NATO-led Resolute Support mission and a separate counter-terrorism effort largely directed at groups such as al Qaeda and Islamic State.

Some 8,000 troops from 38 other countries also participate in Resolute Support.

SIGAR's report also found that Afghanistan's security forces struggled to take the fight to the Taliban, relying on U.S. support for more than half their ground operations.

SIGAR also highlighted a slight increase in the number of casualties among Afghan military members, who have sustained massive losses over the past five years.