Greek taxi drivers, hospital doctors and dentists walked off the job Thursday at the start of a new round of anti-austerity protests by professional groups and labor unions in the debt-ridden country.

The strikes came as Greece faced more criticism from its European partners over its slow pace of reforms and missed targets laid out in bailout agreements which are preventing the country from defaulting.

Taxi drivers were on a 24-hour strike against plans to open up their profession to more competition, and were to hold another daylong walkout over the weekend, while dentists and state hospital doctors began a two-day strike against reforms affecting their profession.

More strikes from the likes of garbage collectors, teachers and tax office workers, are expected in the coming weeks. Scuffles broke out amongst protesters during a demonstration by a few thousand university students, with state media saying one of its camera crews was attacked, leaving one person with minor injuries. Police said the windows of three shops and a post office were smashed.

Greece's Socialist government is stepping up spending cuts, under pressure from international lenders who have seen the country miss targets necessary for it to continue receiving loans from its bailout fund.

After years of overspending and waste, the country found itself unable to service its debts, and has been relying since May 2010 on funds from a euro110 billion ($154 billion) package of rescue loans from other eurozone countries and the International Monetary Fund. In July, European leaders agreed on a second, euro109 billion bailout with more favorable repayment terms for the country, after it became clear the first package would not be enough.

But the country has been struggling to meet the revenue and reform targets set in the bailout agreement. International debt inspectors left Athens last week during a bailout review amid disagreement over the country's deficit figures for this year and 2012.

German Finance Minister Wolfgang Schaeuble warned that Greece's financial situation is "teetering on a knife's blade."

Speaking to lawmakers from Germany's parliamentary budget committee Thursday, Schaeuble warned the Greek government must reduce its debt if it was to receive the next installment of its rescue loans.

The finance minister said he expects the so-called troika to return to Athens in about two weeks. The group left abruptly at the end of last week.

"There is no wiggle room, if Greece cannot present the appropriate numbers," a parliamentary publication quoted Schaeuble as saying.

On Wednesday, Jean-Claude Juncker, who heads the group of eurozone finance ministers, said Greece might not get its next, euro8 billion batch of loans this month if it did not meet its targets. Without the funds, the country would default on its debts within weeks.

The government has already taken a series of cost-cutting measures, including trimming public sector salaries and pensions and a series of tax hikes, but has been falling behind on its revenues in particular. Officials have argued that its figures are being affected by a deeper than expected recession.

The country's statistics agency said Thursday that preliminary data showed gross domestic product in the second quarter of the year contracted by 7.3 percent compared to the same quarter in 2010. The figure was based on non-seasonally adjusted data, the agency said, and was worse than a flash estimate of a 6.9 percent reduction, if slightly better than the 8.1 percent contraction recorded in the first three months of the year.

"The second-quarter figures show that the Greek economy is in dire straits," said IHS Global Insight economist Diego Iscaro.

And with a less upbeat assessment of the global economy into next year, Iscaro warned that the Greek economy would likely remain "in the doldrums for a significant period."

A less rosy global economic picture is bad for Greece as it hits exports at a time when domestic demand is under pressure from high unemployment, tight credit conditions as well as the austerity measures, Iscaro added.

The statistics agency also said unemployment dipped slightly in June, reaching 16 percent compared to May's record high of 16.6 percent in May. A year ago, the unemployment rate was 11.6 percent.

A total 793,000 Greeks were without a job in June 2011, 29,034 fewer than the previous month. The improvement is likely linked to the start of the peak tourism season.

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Melissa Eddy in Berlin contributed.