A bus carrying Turkish pilgrims came under fire in neighboring Syria as they were traveling back from the hajj, leaving two injured and prompting harsh words from Turkey's prime minister.

The incident has increased the already mounting Turkish and international pressure on the government of Bashar al-Assad for its deadly crackdown on pro-democracy protesters, as fresh violence on Monday left 16 dead, according to activists.

Turkish NTV news channel reported on Monday that a bus driver and pilgrim were wounded in the attack at a checkpoint just across the Syrian border. The bus was part of a three-bus convoy returning from Saudi Arabia.

A video posted online showed the apparent aftermath of the attack, including several shattered windows and one person being carried on a stretcher by ambulance staff.

Passengers on the bus said they had been told to disembark at a checkpoint by up to eight uniformed Syrian soldiers.

"They were hidden in their hideouts ... these were soldiers, these were not civilians, their flags were there," a male passenger in his thirties said.

"One of the soldiers said 'Come, come', he wanted to get me inside, I didn't go inside," the passenger said.

"I had nothing in my hands, there were seven or eight of them. He cocked his gun at me and said 'Put your hands up'...I shouted for everyone to run, we ran and they started firing at our backs. God saved us," he said.

The wounded were being treated in a hospital in Antakya, just across the border in Turkey's Hatay province.

Raised tensions

Recep Tayyip Erdogan, Turkey's prime minister, warned in a statement on Monday that Syrian President Assad's time in power is limited.

"You can maintain your grip on power in Syria with tanks and cannons, but one day you will be gone," he said.

Tensions have been running high between Syria and Turkey as Ankara has become increasingly vocal in its criticism of Damascus' crackdown on protests against his regime.

According to a UN report, 3,500 people have been killed in state violence since protests began in mid-March.

In the latest wave of violence, the Syrian Revolution General Commission said 16 civilians were killed by security forces and armed Assad loyalists on Monday.

The western city of Homs, a hub of protests, was the worst hit, with 13 casualties. Two people were killed in Hama and one in Idlib, the Commission said.

Al Jazeera's Hashem Ahelbarra, reporting from Istanbul, said: "This is something which is definitely going to add to the already strained ties between Ankara and Damascus.

"Turkey is a pivotal country in the attempts by the international community to enforce regime change in Syria. They look at what's happened now as retaliation by the Syrian government, but they are very cautious at this particular moment."

Increased pressure

In other developments, William Hague, the British foreign secretary, said on Monday that the international community would do as much as it could to raise the pressure on Syria, and said the possibility of a further tightening of sanctions was under discussion.

"We will increase the pressure on the Assad regime. I discussed this with the Secretary of the Arab League yesterday and I believe they will wish to do so at their further meeting tomorrow," he told BBC radio in an interview.

"The behavior of that regime is appalling and unacceptable and of course we will do what we can to support democracy in Syria in the future."

Hague will meet representatives of various Syrian opposition groups in London later on Monday in an intensification of
contacts with opponents of Assad.

"We're not at the point of a formal recognition of them... partly because there are differing groups; there isn't a single national council as there was in Libya... and the international community has not yet reached that point."

PHOTO CAPTION

Turkey's Prime Minister Recep Tayyip Erdogan

Al Jazeera