KABUL, Afghanistan -- A wave of violence continued across Afghanistan Tuesday with Taliban insurgents killing Afghan soldiers in the northwest of the country as the Canadian embassy warned Canadians to leave for their own safety.

Insurgents have stepped up attacks on the Afghan capital in recent weeks, specifically targeting foreigners. Since last Thursday, four foreigners, including a British embassy employee, have been killed in attacks claimed by the Taliban.

The U.S. embassy said a van disguised as a Red Cross ambulance was "allegedly planning to conduct a (car bomb) attack against Western convoys or facilities in the Wazir Akbar Khan" diplomatic area.

A guesthouse occupied by a U.S. contractor, Aecomm, was attacked in the neighbourhood on Thursday, hours after a suicide attack on a British embassy vehicle killed one British security guard and an Afghan driver.

On Saturday, three South Africans -- a father and his son and daughter -- and an Afghan were killed in an attack on the Kabul office of California-based charity Partnership in Academics and Development.

Afghan officials expect December to be a tense month, as President Ashraf Ghani consolidates relationships with Washington and NATO after signing bilateral security agreements allowing an enduring military presence after the combat mission formally ends on Dec. 31.

Ghani was in Brussels to meet NATO foreign ministers on Tuesday, and will later travel to London for a two-day meeting of international donors.

The Canadian embassy warned citizens that the "threat to foreigners, including Canadians, from terrorist and criminal violence is extremely high."

"If you are already in Afghanistan, you should leave," the advisory said, adding anyone travelling in Afghanistan "is taking a serious risk."

Six Afghan soldiers were killed in the north-western province of Badghis after insurgents launched several attacks on guard posts.

Gen. Douod Shah Wafa, provincial commander of the Afghan National Army, says Taliban used machine-guns and rocket-propelled grenades to attack the posts in Bala Murghab district early Tuesday. He said three insurgents were killed.

In eastern Afghanistan, an American drone killed five insurgents in Shirzad district in Nangahar province, said Ahmad Zia Abdulzai , the provincial governor's spokesman.