By Wiktor Szary

WARSAW (Reuters) - Poland's parliament tightened anti-terrorism laws on Friday ahead of hosting two high-profile events, giving security forces the right to more closely monitor the movements of foreign citizens and hold suspects for longer without charges.

Poland is one of several eastern European states reviewing its anti-terror laws in the wake of the Islamist attacks in Brussels in March, signaling the region's growing concern that it may no longer be immune to the threat.

In early July, heads of NATO members, including U.S. President Barack Obama, will hold a summit in Warsaw at which they are likely to agree to deploy more troops on the alliance's eastern flank to counter Russia's renewed assertiveness.

Two weeks later, the southern city of Krakow will host the World Youth Day, a Catholic celebration due to be attended by Pope Francis and some two million pilgrims from across the world.

Both events pose a clear terrorism risk, experts say.

"Poland does not face any immediate threats from Islamist militants, but we are no longer an anonymous country for them," a high-rank security source told Reuters on condition of anonymity.

The ruling conservative Law and Justice (PiS) party says the new legislation is needed to address those threats.

The new law gives the state security service the right to conduct surveillance of foreign citizens for up to three months without prior court approval.

It allows for suspects to be held for 14 days without charges but with court approval, expanding the current period of 48 hours a suspect can be held without charges.

The regulation also makes it easier for foreigners to be deported if considered a threat, and regulates the sale and usage of pay-as-you-go SIM cards, which are now sold freely and anonymously.

Critics say the legislation gives the secret services excessive powers, and see the move as part of the ruling party's efforts to strengthen its grip on key institutions.

Rights group Amnesty International described the bill as dangerous, saying it gives "seemingly unlimited powers" to Poland's intelligence services.

In order to become law, the bill must be approved by the upper chamber of parliament, where PiS also has a majority, and be signed into force by the president - both likely to be a formality.

Separately, a pan-European rights body recommended on Friday that Poland introduce more checks to the surveillance powers of police under another law amended by the ruling party.

(Additional reporting by Pawel Sobczak; Editing by Richard Balmforth)