KABUL - Three British paratroopers and an American service member were killed in attacks in Afghanistan's south and east, officials said Friday, raising the number of international troops slain in the first week of August to 19.

The pace of Western casualties could make August the deadliest month for U.S. and allied forces in Afghanistan since the start of the nearly eight-year war.

NATO and the British government said the paratroopers' armoured vehicle was hit by a roadside bomb during a patrol with Afghan forces north of Lashkar Gah in the southern province of Helmand on Thursday. Taliban insurgents then opened fire. The soldiers fired back but the three were killed and one was critically wounded, officials said.

NATO also said an American service member was killed in an attack on a convoy Friday morning in eastern Afghanistan. The alliance did not immediately provide further details.

Attacks killed at least 75 troops from the U.S. and other international military forces in July, the highest death toll for a single month since 2001, according to military reports.

Thousands of additional U.S. Marines have been deployed to southern Afghanistan -- the Taliban's heartland -- in an attempt to reverse the militants' gains and enable Aug. 20 presidential elections to take place.

President Hamid Karzai, the leading candidate, held his first major campaign rally in the capital Friday, drawing thousands of cheering supporters, many members of the Shiite Muslim Hazara minority.

He said his administration had opened new educational opportunities for young Afghans, and encouraged the Hazara to vote despite Taliban threats to disrupt the election.

"Relax," he said. "God willing, everything will go safely."

Many Hazaras, believed to make up more than 10 per cent of the population, voted for Karzai in the country's last presidential election. He has courted them by appointing Hazara officials to important ministries and other government posts. Hazara leader Karim Khalili is currently the second vice-president.

Karzai was long seen as the inevitable winner, but Abdullah Abdullah, a former foreign minister, has emerged as Karzai's top challenger and appears to have closed at least part of the gap with a campaign focusing on government mismanagement, corruption and rising violence.

Meanwhile, NATO's new secretary-general said the alliance needs more troops in Afghanistan if its mission is to be successful.

Secretary-General Anders Fogh Rasmussen told the BBC from Afghanistan that NATO progress in fighting the Taliban insurgents in southern Afghanistan this summer has come because troop levels in the region have increased.

U.S. officials have said commanders are likely to ask for more troops after they complete a report on how to turn the war in Afghanistan around.

Afghan officials said roadside bombs killed five policemen and an Afghan guard in the south, where thousands of new U.S. and British forces are trying to secure roads and population centres ahead of the election.

The insurgents have dramatically increased their use of roadside bombs against foreign and Afghan forces.

The policemen were killed when their vehicle hit a buried bomb in Kandahar's Arghandab district late Thursday, said Abdul Jabar, the district chief.

Another blast Friday in Kandahar's Zhari district killed an Afghan guard escorting a NATO supply convoy, said Niaz Mohammad Sarhadi, a local official. Four other guards were wounded, he said.

An airstrike in Zabul, another southern province, killed three suspected militants who were planting a bomb on a road Thursday, said Ghulam Jelani Farahi, Zabul's deputy provincial police chief.