SAN SALVADOR, El Salvador (AP) — Paula Cruz wept quietly at the foreign ministry office in El Salvador’s capital after reporting that her son was missing — apparently kidnapped — in Mexico.

“I got a phone call asking me to send $2,500 to ransom him,” the 77-year-old mother said, clutching the last letter she received from her 43-year-old son. “I didn’t have the money. I don’t know if he is alive or dead.”

Cruz fears her son may be one the 72 migrants found shot to death in northern Mexico last week. She is one of hundreds of people who streamed to government offices in Central America after news of the massacre spread, searching for news of relatives who went missing after setting out through Mexico hoping to reach the United States.

In the overwhelming majority of cases, family members’ descriptions did not match the bullet-ridden bodies found in heaps at a ranch in the state of Tamaulipas. Instead, rights workers say, the missing migrants may be part of a huge toll of hundreds, and perhaps thousands, of migrants killed by organized crime gangs and whose bodies may have been hacked up, dissolved in acid or buried in unmarked paupers graves.

The true number of undocumented migrants killed in Mexico in recent years may never be known, but they would almost certainly dwarf the number discovered last week. Mexico’s National Human Rights Commission said there were witness accounts of 198 mass kidnappings involving 9,758 migrants in a six month-period in 2009.

Just Tuesday, police in the Mexican resort of Cancun rescued six Cuban migrants who had been captured by a gang and were being held prisoner in a house near the city’s airport, said Quintana Roo state police director Enrique Alberto Sanmiguel. He said the captors were demanding $8,000 to $10,000 from the Cubans’ families in the United States.

Activists say drug cartels like Mexico’s Zetas — the gang blamed in the Tamaulipas massacre — frequently kill one or two from each group to scare the rest into asking relatives to meet ransom demands.

Almost 200 relatives showed up at the offices of the Honduras’ foreign ministry in Tegucigalpa saying their loved ones had disappeared somewhere in Mexico. So far only 21 bodies found at the massacre site have been identified as Hondurans; 19 are of other nationalities, and 32 are unidentified.

In Guatemala, relatives have called the country’s foreign ministry to report about 30 missing migrants since the massacre.

El Salvador’s foreign ministry says at least 91 families have shown up in the capital, and at Salvadoran embassies and consulates in the United States, to report missing relatives since the massacre. The missing migrants had set out to cross Mexico months ago — in some cases, years ago.

Rosa Centeno was one of those who lined up at the El Salvador foreign ministry office. She was looking for her husband, Salvador Carpio, 47.

“I haven’t heard anything from him in a week. The last time we talked he was in Tamaulipas,” Centeno said. “Some men called and asked for $400, and I sent it.”

Some of the relatives covered their faces outside the offices out of fear of drawing further attention from kidnappers or endangering their missing relatives.

“They called and told us that they had my brother,” said one man, who would give his name only as Salvador. “They asked us for contacts (of relatives) in the United States to pay $10,000 in ransom.”

Salvador said the family later got a horrifying call. “Last Saturday the same man called and said my brother was among the dead.”

Alberto Xicotencatl, who runs a migrant shelter a block from railway lines used by migrants in the northern Mexico city of Saltillo, said drug cartels frequently torture and kill one or two from each group to scare the rest into dunning money from relatives for ransom.

Given the estimates on kidnappings that would amount to hundreds killed each year. Others are killed in robberies, assaults and rapes.

“The estimates are that in the cemeteries of Tapachula (a city near Mexico’s southern border with Guatemala), there are hundreds of unidentified bodies, of migrants, that wind up in paupers’ graves,” Xicotencatl said.

Tapachula officials were not immediately available to comment. But the spokesman for Arriaga, another Chiapas railway town, Alfredo Ovilla, said there may be as many as 50 to 100 migrants in graves there after violence in earlier years targeted those riding trains. He said increased police and migrant-protection patrols had reduced the violence.

On Tuesday, Mexico announced the outlines of a plan to reduce violence against migrants, by helping build more shelters, keeping a closer watch on railway lines on which migrants travel, and using information campaigns “to discourage undocumented migration” and inform migrants of their rights.

Mexico’s Foreign Relations Department could not provide figures on the number of foreign migrants reported missing or dead in the country, though it keeps a careful accounting of Mexican migrants found dead in the southwestern United States — 369 in 2009.

Many of the Central American migrants’ home countries also don’t keep track of those missing in Mexico.

Andrea Furlan, a spokeswoman for Guatemala’s foreign ministry, said reports come in of migrants being tortured or raped or having disappeared, but seldom with the detail that would allow authorities to take action.

“People are not in the habit of filing crime reports,” Furlan said.

Xicotencatl said there is no firm estimate of the number of migrants killed in Mexico and “we will probably never have it,” given that — unlike the Tamaulipas massacre — many of the bodies may never be found.

He said migrants have told about seeing fellow migrants killed “and then chopped up and put into barrels with acid, so that there is no evidence.”

Still, some good might come of the massacre. Some Central American countries have set up special offices or hot lines for families report disappearances and might keep them working even after the last of the massacre victims are identified.

“We in the support network and civic groups really lament this situation very much,” Xicotencatl said of the mass killing, “but it may have been just the push people needed to begin to see what is really happening.”

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Associated Press Writer Mark Stevenson contributed to this report from Mexico City.