Pakistan summoned an Indian envoy to formally complain Thursday about alleged violations of its airspace as it sought to deflect heat from the deadly Mumbai terrorist attacks onto its longtime rival.

In a sign of growing pressure on Islamabad to harden its foreign policy, thousands protested against allowing U.S. forces to ship supplies through Pakistan into Afghanistan.

Pakistani leaders had previously downplayed the alleged breaches by Indian aircraft, calling them "technical."

But after days on the defensive over signs that Pakistani nationals staged the attacks that killed 164 in India's commercial capital, Islamabad appeared to be taking a more aggressive tack.

On Wednesday, they stepped up demands that India show evidence to back its claims that a Pakistani militant group trained and sent the gunmen, saying court prosecutions would be impossible without proof.

Indian Deputy High Commissioner Manpreet Vohra said Thursday that he will pass on the complaint over the alleged airspace violation to his government, but he noted previous Indian denials.

"Our government, after holding an inquiry, has already said that there was no airspace violation from our side, and I reiterated this stance today," Vohra told The Associated Press.

Pakistan had said earlier that the two separate violations occurred Saturday over the eastern city of Lahore and Pakistan-controlled Kashmir.

The Indian aircraft allegedly flew some one to three miles into Pakistan. Pakistani fighter jets chased them back over the border, according to the Pakistan Air Force.

In a statement Thursday, the Foreign Ministry said "technical and airspace violations" occurred on Friday and Saturday, violating a 1991 bilateral agreement. It did not elaborate and a spokesman could not immediately be reached to explain the discrepancy.

Pakistan and India are both nuclear-armed nations who already have fought three wars against each other. The Mumbai attacks have strained diplomatic relations and halted an already slow-moving peace process between the countries.

India says the Pakistan-based Lashkar-e-Taiba militant group was behind November's attacks. Pakistan has arrested some suspects and clamped down on a charity allegedly linked to the outlawed group, but it insists it needs evidence from India.

Asked about that demand, Vohra said Thursday that India "will do it only once our investigations are complete."

Pakistani opposition politicians and commentators are increasingly critical of the government for moving against Jamaat-ud-Dawa without making public any evidence showing wrongdoing.

It is also under pressure from religious parties for failing to persuade the U.S. to halt cross-border missile strikes on militant targets in Pakistan's northwest.

On Thursday, several thousand activists with Jamaat-e-Islami, a hard-line Islamist party, protested Thursday against the strikes as well as NATO and U.S. troops' use of a supply route that runs through Pakistan into Afghanistan.

It appeared to be the largest rally against Western use of the route since the government took office in March and one of the largest anti-government protests so far. Militants have attacked trucks using the critical Khyber Pass route several times in recent weeks.

Protesters bearing placards and banners marched along a key road in the main northwestern city of Peshawar, led by party leader Qazi Hussain Ahmed. The protesters also criticized Pakistani military offensives against Al Qaeda and Taliban insurgents near the Afghan border.